tag:theconversation.com,2011:/africa/topics/solar-system-1032/articlesSolar system – The Conversation2018-08-10T05:17:18Ztag:theconversation.com,2011:article/1013242018-08-10T05:17:18Z2018-08-10T05:17:18ZJupiter's magnetic fields may stop its wind bands from going deep into the gas giant<figure><img src="https://images.theconversation.com/files/231414/original/file-20180810-30443-kel1zv.jpg?ixlib=rb-1.1.0&amp;rect=1441%2C0%2C1891%2C1287&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">The colorful cloud belts dominate Jupiter’s southern hemisphere in this image captured by NASA’s Juno spacecraft.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/pia21974/jupiter-s-colorful-cloud-belts">NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill</a></span></figcaption></figure><p>One of the most striking features of <a href="https://solarsystem.nasa.gov/planets/jupiter/overview/">Jupiter</a> – a gaseous giant with no solid surface – is the coloured bands that encircle the planet. </p>
<p>These bands are so large and distinct that they can be seen from here on Earth using a modest telescope, and thus have fascinated astronomers since the era of Galileo.</p>
<p>In research <a href="https://doi.org/10.3847/1538-4357/aace53">published today in The Astrophysical Journal</a>, Jeffrey Parker, from Lawrence Livermore National Laboratory in the United States, and I have developed a theory that could help explain what is going on beneath these bands and why they only go so deep into the planet.</p>
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<span class="caption">The bands of Jupiter captured by an Earth-based astronomer.</span>
<span class="attribution"><span class="source">NASA/Freddy Willems</span></span>
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<h2>Winds on Jupiter</h2>
<p>These bands are actually strong steady winds, or jets, that flow in Jupiter’s atmosphere, carrying with them clouds of ammonia and other colourful elements. These jets are similar to the jet streams that flow high up in Earth’s atmosphere. </p>
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<a href="http://theconversation.com/jupiters-new-moons-an-irregular-bunch-with-an-extra-oddball-thats-the-smallest-discovered-so-far-100160">Jupiter's new moons: an irregular bunch with an extra oddball that's the smallest discovered so far</a>
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<p>But there is more to these jets than meets the eye. What goes on below Jupiter’s clouds is, to a large extent, still a mystery.</p>
<p>Although there exist many theories for how the jets on Jupiter form and how deep they penetrate beneath the clouds, until recently we had no direct observations to support them.</p>
<p>In mid-2016, NASA’s spacecraft Juno headed to Jupiter with a mission to approach the planet closer that any probe has done before. It reached distances of less than 4,500km above Jupiter’s clouds at its closest approach (about the distance from New York to Los Angeles).</p>
<p>Upon arrival, Juno began to make precise measurements of Jupiter’s gravitational and magnetic fields. </p>
<p>When the data started pouring in, it was found that the jets go <a href="https://www.theguardian.com/science/2018/mar/07/nasa-spacecraft-reveals-jupiters-interior-in-unprecedented-detail">as deep as 3,000km</a> beneath Jupiter’s clouds, and then terminate. (This is about 5% of the planet’s <a href="https://solarsystem.nasa.gov/planets/jupiter/by-the-numbers/">radius at the equator</a>.)</p>
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<figcaption><span class="caption">Only so deep for Jupiter’s bands.</span></figcaption>
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<p>This created a new puzzle for scientists: why do the jets penetrate as deep as they do, but no deeper?</p>
<p>Here is where <a href="https://doi.org/10.3847/1538-4357/aace53">our research</a> comes into the picture. We have developed a theory that explains how magnetic fields have a tendency to shut down the jets.</p>
<p>What does this have to do with Jupiter?</p>
<h2>Inside the gas giant</h2>
<p>Jupiter’s gaseous bulk consists mostly of hydrogen and helium. As you go deep beneath the clouds into the interior, the pressure of the gas increases (similar to how the pressure increases when you dive deep into the ocean here on Earth).</p>
<p>Scientists understand that at about 3,000km below Jupiter’s clouds, the pressure is so high that electrons can get loose from the molecules of hydrogen and helium and start to move around freely, creating electric and magnetic fields.</p>
<p>Is it just a coincidence that this happens at about the same depth that the jets break down? Scientists speculate that it is not. As Steve Levin, Juno project scientist at NASA’s Jet Propulsion Laboratory, <a href="https://youtu.be/S6Joupv6f-M?t=37m3s">explains</a>:</p>
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<p>It’s very interesting that (the jets disappear at) about 3,000km, because that’s about where it might be conducting electricity enough to make a magnetic field.</p>
<p>So, it could be that the magnetic field has something to do with why the belts and zones only go that deep (…) But we don’t know this yet; this is just speculation.</p>
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<p>Here is how our theory ties in. Using principles from statistical physics of turbulent systems, we devised a mathematical model which predicts that when magnetic fields are strong enough, the jets shut down.</p>
<p>Specifically, within our model a jet organises magnetic fluctuations in such a manner so that the coherent effect of these fluctuations acts to dampen the jet itself.</p>
<p>This offers a partial explanation as to why the jets terminate at about 3,000km below the clouds.</p>
<p>It’s hoped that theory and observation together will continue to give deeper insight on the physics of the universe as Juno and other probes, such as <a href="https://blogs.nasa.gov/parkersolarprobe/2018/08/09/parker-solar-probe-proceeds-toward-launch-aug-11/">NASA’s new Parker Solar Probe</a>, explore and gather data from our Solar system and beyond.</p><img src="https://counter.theconversation.com/content/101324/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Research was supported by the U.S. National Science Foundation grants PHY-1607611 and OCE-1357047. Also by the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. DE-AC52-07NA27344.</span></em></p>Jupiter's bands are one of its most striking features – and can be seen from Earth – but they only go so deep within the giant planet. Now scientists think they know why.Navid Constantinou, Research fellow and researcher in climate and fluid physics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1005232018-07-25T14:02:02Z2018-07-25T14:02:02ZDiscovered: a huge liquid water lake beneath the southern pole of Mars<figure><img src="https://images.theconversation.com/files/229230/original/file-20180725-194134-1xuput9.jpg?ixlib=rb-1.1.0&amp;rect=0%2C0%2C1690%2C1105&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Mars&#39; south polar cap, as seen from Mars Global Surveyor. Buried beneath, we now know, is a lake of liquid water.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA02393">NASA/JPL/MSSS</a></span></figcaption></figure><p>We now know that there is permanent liquid water on Mars, according to a <a href="http://dx.doi.org/10.1126/science.aar7268">paper published today</a> in the journal Science.</p>
<p>This new finding comes from research using the <a href="http://sci.esa.int/mars-express/">Mars Express</a> spacecraft that has been orbiting the red planet since December 25, 2003. </p>
<p>One of the suite of instruments carried by Mars Express is MARSIS (the <a href="https://mars.jpl.nasa.gov/express/mission/sc_science_marsis01.html">Mars Advanced Radar for Subsurface and Ionosphere Sounding</a>), which allows researchers to use radar to study features beneath the planet’s surface.</p>
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<a href="http://theconversation.com/there-is-water-on-mars-but-what-does-this-mean-for-life-48310">There is water on Mars, but what does this mean for life?</a>
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<p>Using observations spanning a period of four years, a team of researchers from Italy found evidence of a large lake of salty water, buried 1.5 kilometres beneath Mars’ southern polar cap. That lake is at least 20 kilometres across, and seems to be a permanent feature.</p>
<h2>More than droplets</h2>
<p>The reason people are excited about this discovery is because on Earth, everywhere you find liquid water, you find life. NASA has long espoused a philosophy of “<a href="https://www.nasa.gov/vision/earth/everydaylife/jamestown-water-fs.html">follow the water</a>” in its program of <a href="https://astrobiology.nasa.gov/">astrobiological research</a> – trying to answer the question “are we alone?”</p>
<p>Over the past two decades, we have seen mission after mission travel to Mars. Some, like Mars Express, are orbiters, whereas others (such as the incredible <a href="https://www.jpl.nasa.gov/missions/mars-exploration-rover-spirit-mer/">Spirit</a> and <a href="https://www.jpl.nasa.gov/missions/mars-exploration-rover-opportunity-mer/">Opportunity</a>) are rovers. A unifying theme across those missions has been their attempts to see whether Mars once had the right conditions for life to exist and thrive.</p>
<p>Through them we have found <a href="https://theconversation.com/the-lost-ocean-of-mars-38739">abundant evidence that Mars was once warm and wet</a>. We also have evidence that <a href="https://theconversation.com/there-is-water-on-mars-but-what-does-this-mean-for-life-48310">liquid water can still be found on the surface of Mars</a>, from time to time. </p>
<p>But until today, the evidence of modern water all pointed towards fleeting moments - <a href="https://www.space.com/6394-phoenix-mars-lander-liquid-water-scientists.html">droplets condensing on the Mars Phoenix lander</a>; or evidence of <a href="https://theconversation.com/nasa-streaks-of-salt-on-mars-mean-flowing-water-and-raise-new-hopes-of-finding-life-48182">brief outflows of salty water in Martian valleys</a>.</p>
<p>Compared with today’s discovery, those earlier findings are a drop in the ocean.</p>
<h2>Mars has a lake</h2>
<p>The latest observations reveal something remarkable: a salty lake buried deep beneath the ice, which seems to be a permanent feature rather than a transient phenomenon.</p>
<p>The comparison that springs to mind are the myriad lakes buried under the ice of Antarctica. So far <a href="http://rsta.royalsocietypublishing.org/content/374/2059/20140306">more than 400</a> such lakes have been found <a href="https://theconversation.com/what-lies-beneath-antarcticas-ice-lakes-life-and-the-grandest-of-canyons-61748">beneath the surface of the frozen continent</a>. </p>
<p>Perhaps the most famous is <a href="http://www.sciencemag.org/news/2013/07/what-s-really-going-lake-vostok">Lake Vostok</a> – one of the world’s largest lakes, buried and hidden away. But the one to which I want to draw your attention is named Lake Whillans.</p>
<p>Lake Whillans is buried some 800 metres below the ice in West Antarctica. In 2013, a team of researchers <a href="https://www.bbc.com/news/science-environment-21231380">succeeded in drilling down into the lake</a> and recovering samples. What did they find? That it was <a href="https://theconversation.com/what-lies-beneath-antarcticas-ice-lakes-life-and-the-grandest-of-canyons-61748">teeming with microbial life</a>. </p>
<p>In other words, the best Earth-based analogues for the newly discovered Martian lake are not just habitable, they are <em>inhabited</em>. Where there’s water, there’s life.</p>
<h2>Is there life on Mars?</h2>
<p>Finding this new lake, buried beneath Mars’ south pole, is another exciting step on our journey of discovery of the red planet. Could there be life there, beneath the ice?</p>
<p>The short answer is that we still don’t know. But it seems like the ideal place to look. What we <em>do</em> know is:</p>
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<li><p>Mars was once warm and wet, potentially with oceans, lakes, and rivers</p></li>
<li><p>On Earth, where you find water, you find life</p></li>
<li><p>The transition from warm, wet Mars to the cold and barren Mars we see today occurred over millions of years</p></li>
<li><p>Life adapts to changing environments, so long as that change is not too fast or dramatic.</p></li>
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<p>So what do you get if you put all that together? Well, this is where things get speculative. </p>
<p>But let’s imagine that in the far distant past, Mars had life. Perhaps the life originated there, or <a href="https://cosmosmagazine.com/biology/over-our-heads-a-brief-history-of-panspermia">maybe it was delivered from Earth, hitching a ride on a meteorite</a>.</p>
<p>Once life is established, it is amazingly hard to get rid of. Over millions of years, Mars cooled and its water became locked in permafrost. Its atmosphere thinned and it became <a href="http://www.midnightplanets.com/">the red planet we see today</a>.</p>
<p>But maybe, just maybe, that life would have been able to follow the water - to move underground, where it might have found a niche, in a dark salty lake, buried beneath the ice of Mars’ southern polar cap.</p>
<h2>That’s all well and good, but what next?</h2>
<p>That’s all speculation, but it shows the kind of thought processes that have driven our ongoing exploration of Mars for the past couple of decades. </p>
<p>Now that we know for sure that there is a reservoir of liquid water just beneath the planet’s surface, astronomers around the globe will be thinking of ways to get down to that water to see what’s there.</p>
<p>That is easier said than done. Landing on Mars is challenging at the best of times, and the great majority of missions to date have landed within about 30° latitude of Mars’ equator. The two exceptions are the <a href="https://www.jpl.nasa.gov/missions/viking-2/">Viking 2</a> and <a href="https://www.nasa.gov/mission_pages/phoenix/main/index.html">Phoenix</a> landers, both of which landed in Mars’ northern lowlands. </p>
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<span class="caption">The locations on Mars’ surface visited by landers to date. It is far easier to land near Mars’ equator than its poles.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
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<p>In addition, landing on Mars’ southern hemisphere is harder still. The north is the lowlands and the atmosphere there is markedly thicker, and the surface smoother (as befits, potentially, <a href="http://planetary-mechanics.com/2017/09/17/the-lowlands-of-mars/">the floor of an ancient ocean</a>).</p>
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<a href="http://theconversation.com/before-we-colonise-mars-lets-look-to-our-problems-on-earth-87770">Before we colonise Mars, let's look to our problems on Earth</a>
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<p>To the south, you have less atmosphere to slow your descent and a rougher surface to make your landing harder.</p>
<p>But, while tricky, it is not impossible. And now we have a huge motivation to try. </p>
<p>It would not surprise me if, within a decade, we see missions being designed to visit Mars’ south pole and drill down to this great lake, to see what lurks within.</p><img src="https://counter.theconversation.com/content/100523/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Researchers have found evidence of a large lake of salty water, buried 1.5 kilometres beneath the southern polar ice cap on Mars. So what does that mean for life on the red planet?Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001602018-07-25T04:35:50Z2018-07-25T04:35:50ZJupiter's new moons: an irregular bunch with an extra oddball that's the smallest discovered so far<figure><img src="https://images.theconversation.com/files/228790/original/file-20180723-189335-bt90kx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">A moon shadow on Jupiter, the red planet now has a dozen more moons added to the list or such orbiting bodies.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA21969">NASA/JPL-Caltech/SwRI/MSSS</a></span></figcaption></figure><p><a href="https://solarsystem.nasa.gov/planets/jupiter/overview/">Jupiter</a> is the largest planet in the Solar system and has been <a href="https://solarsystem.nasa.gov/planets/jupiter/exploration/">studied intensively for hundreds of years</a>, so you might think there would be little left to find.</p>
<p>But earlier this month, researchers announced that another <a href="https://carnegiescience.edu/news/dozen-new-moons-jupiter-discovered-including-one-%E2%80%9Coddball%E2%80%9D">12 moons have been added</a> to the number of such bodies orbiting the giant planet.</p>
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<a href="http://theconversation.com/the-latest-from-juno-as-jupiter-appears-bright-in-the-night-sky-96108">The latest from Juno as Jupiter appears bright in the night sky</a>
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<p>That brings the tally for Jupiter to a whopping 79, the most moons for any known planet. But where did these newly discovered moons come from, and what do they tell us about Jupiter and its place in the Solar system?</p>
<h2>Moons: regular and irregular</h2>
<p>The Solar system’s giant planets have two types of moon: regular and irregular. </p>
<p>Regular moons orbit close to their host, follow nearly circular paths, and move in the same plane as the planet’s equator. In some ways, these moons resemble miniature planetary systems, and we think that they formed in much the same manner <a href="https://theconversation.com/pluto-and-its-collision-course-place-in-our-solar-system-43404">as the planets around the Sun</a>. </p>
<p>As the giant planets gathered material from the disk of gas and dust that surrounded the young Sun – a process known as accretion – they were surrounded by their own miniature disks. Within those disks, the regular moons grew, all in the planet’s equatorial plane.</p>
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<span class="caption">Artist’s impression of a protoplanetary disk - a place where planets are born. Around young giant planets, similar disks give birth to regular moons.</span>
<span class="attribution"><span class="source">ESO/L. Calçada</span></span>
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<p>But the irregular moons are another story.</p>
<p>Their orbits are highly eccentric (elliptical) and inclined relative to the plane of their host planet’s equator. Many even move on retrograde orbits, travelling in the opposite direction to the spin and orbital motion of their hosts. And they are located much farther from their planet than their regular cousins. </p>
<h2>Where do the irregulars come from?</h2>
<p>Because of their wild orbits, the irregular moons cannot have formed in the same way as their regular cousins. Instead, they are thought to have been <a href="http://home.dtm.ciw.edu/users/sheppard/pub/Nicholson2008KBOBook.pdf">captured by their host planets as the process of planet formation came to an end</a>. </p>
<p>We think that each giant planet captured just a handful of irregular moons – a number far smaller than we see today. Over the billions of years since, those moons were pummelled and destroyed by passing asteroids and comets, and collisions with other members of their swarm.</p>
<p>The shattered fragments of those ancient satellites form families of smaller moons - the irregulars we see today. For example, among Jupiter’s satellites we see <a href="https://arxiv.org/pdf/1706.01423.pdf">at least four distinct families</a> of irregular moons, each named after their largest member. </p>
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<a href="https://images.theconversation.com/files/228674/original/file-20180721-142435-1j9s0vv.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228674/original/file-20180721-142435-1j9s0vv.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">The motion of Jupiter’s irregular moons around the giant planet. The main plot (bottom, left) shows the orbits looking top-down, while the other (right and top) plots show the movement out of the plane of the system. Moons of the same colour are members of the same family.</span>
<span class="attribution"><span class="source">Christopher Tylor</span></span>
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<h2>What does the new discovery add to our understanding?</h2>
<p>If we consider Jupiter’s moons in terms of their orbital distance, and the direction in which they move, we can break them into three distinct groups. </p>
<p>The first consists of the inner eight moons, including the famous <a href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA01299">Galilean moons</a> Io, Europa, Ganymede and Callisto, whose orbits lie in the plane of Jupiter’s equator, at distances less than 2 million kilometres. </p>
<p>The second group lies significantly farther from the planet, and move on orbits tilted by between 25° and 56° relative to Jupiter’s equator. These are the prograde irregulars - ten moons orbiting at distances between 7 million and 19 million km. Two of the new discoveries are members of this group.</p>
<p>The final and most populous group is the retrograde irregulars - 60 moons located between 19 million and 29 million kilometres from Jupiter, all moving on orbits inclined by between about 140° and 170° to Jupiter’s equator.</p>
<p>In other words, they orbit backwards, in the opposite direction to everything else. Nine of the new discoveries fall into this category.</p>
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<a href="https://images.theconversation.com/files/228382/original/file-20180719-142420-17w9qtk.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228382/original/file-20180719-142420-17w9qtk.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Plot showing the three groups of moons orbiting Jupiter.</span>
<span class="attribution"><span class="source">Carnegie Institution for Science/Roberto Molar-Candamosa</span></span>
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<p>So that covers 11 of our new moons. What of the 12th? Well, it turns out that the most exciting of the new moons is an oddball - an object that does not fit into any of the groups mentioned above. </p>
<h2>The oddball: Valetudo</h2>
<p>The 12th new moon has tentatively been named Valetudo, after Jupiter’s mythological great granddaughter.</p>
<p>Valetudo is the dimmest of the newly discovered moons. At just a kilometre in diameter (or less), it is the smallest Jovian moon found to date. </p>
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<a href="https://images.theconversation.com/files/228519/original/file-20180720-142432-1u1ipnd.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228519/original/file-20180720-142432-1u1ipnd.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">The yellow lines point to the tiny moving speck of light, the newly discovered moon Valetudo.</span>
<span class="attribution"><span class="source">Carnegie Institute for Science</span></span>
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<p>In terms of its orbital distance, Valetudo lies bang in the middle of the retrograde irregulars - some 24 million kilometres from the giant planet. But its orbit is prograde - meaning that it moves in the direction of Jupiter’s rotation, and in the opposite direction to all other satellites in its vicinity.</p>
<p>Valetudo’s size and unusual orbit pose interesting questions.</p>
<p>How did something so small survive in the celestial firing range around Jupiter? </p>
<p>Could Valetudo be the final surviving remnant of a previously uncharted family, whittled to nothing by aeons of headlong flight into the retrograde irregulars? </p>
<p>Are there are other members of the Valetudo family out there, awaiting discovery?</p>
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Read more:
<a href="http://theconversation.com/water-water-everywhere-in-our-solar-system-but-what-does-that-mean-for-life-76315">Water, water, everywhere in our Solar system but what does that mean for life?</a>
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<p>Beyond these questions, Valetudo’s small size offers an important clue to the origin of the Jovian satellite system. Had Valetudo been on its current orbit while Jupiter was still accreting, it would have been too small to resist the drag of the inflowing gas. Like a ping pong ball in a gale, it would have been dragged inwards, to be devoured by the giant planet.</p>
<p>In other words, tiny Valetudo tells us that the process that created the irregular satellite families continued long after the formation of Jupiter was complete. In fact, that process likely continues even now, with occasional collisions tearing moons asunder, to birth new families of irregular worlds. </p>
<p>Who knows? The next such collision might come when Valetudo runs into one of the retrograde irregulars. Given that their orbits cross, it may only be a matter of time.</p><img src="https://counter.theconversation.com/content/100160/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Jupiter now has at least 79 moons, the most for any known planet. But where did these newly discovered moons come from?Jonti Horner, Professor (Astrophysics), University of Southern QueenslandChristopher C.E. Tylor, PhD Candidate, Adjunct Lecturer, Assistant Examiner, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001622018-07-20T07:25:21Z2018-07-20T07:25:21ZCapturing the shadow of Saturn's moon Titan from right here on Earth<figure><img src="https://images.theconversation.com/files/228551/original/file-20180720-142423-5iics4.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">NASA&#39;s Cassini spacecraft captures Saturn&#39;s largest moon, Titan, passes in front of the planet and its rings.</span> <span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/5441/titan-up-front/">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p><a href="https://solarsystem.nasa.gov/moons/saturn-moons/titan/overview/">Titan</a> is <a href="https://solarsystem.nasa.gov/planets/saturn/overview/">Saturn</a>’s largest moon, and it is more like a planet than a moon in many respects.</p>
<p>It has a thick atmosphere as well as wind, rivers, lakes made of hydrocarbons such as methane, and a liquid water ocean. Understanding its atmosphere may help us in the search for life on other planets.</p>
<p>Hence the excitement this July when a rare opportunity was available to further study Titan, from right here on Earth. On July 18 at 11:05pm (WAST, Western Australian time) Titan passed in front of a faint star, as seen by observers across most of Australia.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/the-secrets-of-titan-cassini-searched-for-the-building-blocks-of-life-on-saturns-largest-moon-83441">The secrets of Titan: Cassini searched for the building blocks of life on Saturn's largest moon</a>
</strong>
</em>
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<p>This event, known as an <a href="https://www.space.com/33946-occultations.html">occultation</a>, lasted only a few minutes and about 2% of the star’s light was blocked by Titan’s atmosphere.</p>
<p>The effect was so small it required large telescopes and a special camera to record it. But the data gathered should have profound implications for our understanding of an atmosphere on another world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228381/original/file-20180719-142423-dk5z13.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Saturn’s moon Titan compared (by diameter) to the Earth and its Moon.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Titan,_Earth_%26_Moon_size_comparison.jpg">Wikimedia/The Conversation</a></span>
</figcaption>
</figure>
<h2>Examining Titan’s atmosphere</h2>
<p>Scientists have developed a very clever technique to examine Titan’s atmosphere using stellar occultations. As Titan enters and exits an occultation, the star’s light would illuminate the atmosphere from behind, but be blocked by the moon itself. </p>
<p>Scientists then record subtle changes in brightness of the star over a few minutes, which represents a profile of the atmosphere’s density with height. </p>
<p>This method was used to study Titan’s atmosphere before, during a stellar occultation in 2003.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228150/original/file-20180718-142405-1mq54j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Artist’s concept of Cassini’s June 4, 2010, flyby of Saturn’s moon Titan.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=2625">NASA/JPL</a></span>
</figcaption>
</figure>
<p>But in 2005, when <a href="https://saturn.jpl.nasa.gov/">Cassini’s</a> Huygens lander arrived at Titan and descended to its surface, the atmospheric profile measured from its instruments did not match that derived from the 2003 occultation. This fuelled the question of how variable is the state of Titan’s atmosphere.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228164/original/file-20180718-142417-1hgve61.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Composite of Titans surface taken by Huygens at different heights.</span>
<span class="attribution"><span class="source">ESA/NASA/JPL/University of Arizona</span></span>
</figcaption>
</figure>
<p>Since the Cassini mission ended in 2017, NASA’s Karsten Schindler said there was keen interest in any new atmospheric observations from occultations:</p>
<blockquote>
<p>Occultations remain the only means to study Titan’s upper atmosphere and its evolution for the foreseeable future.</p>
</blockquote>
<h2>Countdown to the July occultation</h2>
<p>So how were the latest observations made, and how was the data gathered?</p>
<p>From the air, the plan was for the July 18 occultation to be recorded by a camera mounted on a telescope of the Stratospheric Observatory of Infrared Astronomy <a href="https://www.nasa.gov/mission_pages/SOFIA/index.html">(SOFIA)</a> on board a Boeing 747 aircraft.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228145/original/file-20180718-142435-pzv82d.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">SOFIA takes off from Christchurch International Airport in 2017.</span>
<span class="attribution"><span class="source">SOFIA/ Waynne Williams</span></span>
</figcaption>
</figure>
<p>That’s right: a telescope mounted inside a modified passenger plane imaging an object more than 1 billion kilometres away! SOFIA would fly above the clouds between Australia and New Zealand.</p>
<p>From the ground, several facilities across Australia were to attempt to record the occultation.</p>
<p>The University of Western Australia’s <a href="http://www.zt.ems.uwa.edu.au/">Zadko Telescope</a>, located about 80km north of Perth (see map, below), was identified by NASA as a ground facility sensitive enough to contribute to the project. </p>
<iframe src="https://www.google.com/maps/embed?pb=!1m14!1m12!1m3!1d2388.822095869977!2d115.71176221504176!3d-31.356613427959715!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!5e1!3m2!1sen!2sau!4v1532067433110" width="100%" height="500" frameborder="0" style="border:0" allowfullscreen=""></iframe>
<p>The most obvious deal breaker was the weather. July is one of the wettest months at the Zadko telescope site. But, as we found out, there were other unforseen challenges. </p>
<h2>Three days to occultation</h2>
<p>NASA’s Karsten Schindler arrived at the UWA research site, at Gingin, on Monday July 16, armed with a case filled with delicate cameras, cables and electronics.</p>
<p>The camera was the key to record the event. The current Zadko telescope camera cannot record fast enough to capture the rapid changes in brightness of the occulted star. </p>
<p>The Zadko Telescope was fitted out with a fast shooting (a frame every few seconds), NASA camera, more like a movie camera than a standard astronomical camera. After hours of installation, the new imaging system needed to be tested.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/228387/original/file-20180719-142420-f10uxn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Ground occultation team: John Kennwell, Arie Verveer, Karsten Schindler with the Zadko Telescope in the background.</span>
</figcaption>
</figure>
<p>Unfortunately, the observatory roof would not open because of a faulty sensor. No Monday test, but hey, we still had Tuesday to test the system? Onsite engineers scrambled to fix the sensor ready for Tuesday.</p>
<h2>Two days to occultation</h2>
<p>On Tuesday, I received the following text message from the site.</p>
<blockquote>
<p>11:07pm: Rain sensor working but clouded out … cheers Arie. So no chance testing the camera and weather forecast for Wednesday was bleak.</p>
</blockquote>
<h2>The day of occultation</h2>
<p>Despite the cloud and nearly constant rain showers, team occulation (Karsten, Arie and John) were on site ready to start pointing the telescope and activate the imaging. </p>
<p>“Up to 10pm it was still raining,” Karsten told me the next morning. “Then a miracle happened.”</p>
<p>Less than an hour before the event, and he said the weather changed.</p>
<p>“The clouds seemed to vaporise away, leaving a totally cloudless sky with 100% visibility. I have never seen anything like it.” </p>
<p>The team swung into action, pointing the telescope at the target star, focusing the camera. At the designated occulation time 11:05pm, Karsten hit the image acquisition button, enabling the camera to take hundreds of images over a few minutes.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/what-cassinis-mission-revealed-about-saturns-known-and-newly-discovered-moons-83430">What Cassini's mission revealed about Saturn's known and newly discovered moons</a>
</strong>
</em>
</p>
<hr>
<p>Eager to see if the data contained the signature of an occulation, the team performed a preliminary analysis within minutes. Yes, there was a clear occulation signature, a big dip in the brightness of the star at exactly the predicted time of the occulation.</p>
<p>Next morning I was informed that SOFIA had also captured the event. </p>
<p>The data recorded from the Australian ground stations and by SOFIA will be analysed over the coming weeks and published in peer reviewed journals.</p>
<p>But one thing the journals won’t highlight is the excitement of the observation, and the enormous effort by a few individuals who helped acquire this data that should hopefully give us a better understanding of the atmosphere of Titan.</p><img src="https://counter.theconversation.com/content/100162/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Coward receives funding from the Australian Research Council Center of Excellence: OzGrav CE170100004
</span></em></p>Titan is more than a billion kilometres from our Sun but occasionally it's shadow can be seen here on Earth, with the right technology. That's what scientists gathered in Western Australia to observe.David Coward, Associate professor, University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/996782018-07-11T11:29:08Z2018-07-11T11:29:08ZRare meteorite recovery in Botswana can help reveal secrets of outer space<figure><img src="https://images.theconversation.com/files/226908/original/file-20180710-70039-1yiqj4v.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Fragments of the asteroid 2018 LA scattered over a wide area in Botswana&#39;s Central Kalahari Game Reserve.</span> <span class="attribution"><span class="source">Alexander Proyer</span></span></figcaption></figure><p>A meteorite <a href="http://earthsky.org/human-world/asteroid-2018-la-fragments-meteorites-south-africa">has been</a> recovered from a remote area of Botswana. The event is one of a kind as the meteor was identified before entering the atmosphere, and its fall and retrieval documented. It’s only the second time this has happened. The Conversation Africa’s Moina Spooner spoke to Fulvio Franchi and Alexander Proyer about their mission to retrieve the meteorite and why it matters.</p>
<hr>
<p><strong>Why is the find in Botswana such a big deal?</strong> </p>
<p><em><strong>Alexander Proyer:</strong></em> Meteorites are fragments of asteroids or comets fallen on the surface of earth. Finding a fresh one is rare but what makes this case really sensational, is not the fall itself but the fact that we knew it was coming. Usually, people are taken by surprise, seeing a flash of light or fireball when the asteroid enters the atmosphere. But this one was observed in space, eight hours before it collided with Earth.</p>
<p>The asteroid was first detected by a network of observatories – the <a href="https://www.nasa.gov/planetarydefense/">NASA’s Planetary Defence network</a> – that search the night-sky for so-called ‘near-earth objects’. In this case it was Richard Kowalski of the <a href="https://catalina.lpl.arizona.edu/">Catalina Sky Survey</a> in Arizona, who discovered the extremely dim light of a moving object out in space. </p>
<p>This was only the third time in history that such an early observation and prediction was possible and only the second time a fragment was recovered. The first find was from an asteroid <a href="https://www.space.com/13215-triple-asteroid-collision-sudan-meteorites.html">called</a> TC3 in Sudan.</p>
<p><em><strong>Fulvio Franchi:</strong></em> We can consider this event as a free-of-charge delivery of material from space that would otherwise require a highly expensive space mission to recover. </p>
<p>Most meteorites are extremely old rocks, <a href="https://mobile.arc.nasa.gov/public/iexplore/missions/pages/yss/november.html">dating back</a> to the birth of the solar system about 4.56 billion years ago, and originate from the <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/asteroids.html">asteroid belt</a> – objects small and large that consist of stone, metal and carbon, which orbit in the space between Mars and Jupiter. These asteroids keep a “record” of planet-forming processes – like growth by gravitational attraction, heating and melting – a record that is no longer available on Earth because it was overprinted by the tectonic processes operating on our home planet. </p>
<p>Other meteorites are fragments from our Moon or from Mars, that were catapulted into space by major impact events. They are even rarer than regular asteroids. One can appreciate the value of these asteroids by just considering the costs of a space mission to the Moon, Mars or even the asteroid belt, to obtain such samples. This find is a real gift for the international consortium, currently forming to perform laboratory analyses of this and other fragments still to be found during the continuing search. </p>
<p><strong>What happened after it was first detected?</strong></p>
<p><em><strong>Alexander Proyer:</strong></em> After Kowalski in Arizona saw it, he alerted other institutions, that are part of NASA’s Planetary Defense network, and they worked out the size and trajectory of the body, concluding that an asteroid 2-3 meters in diameter was about to hit Earth – in Botswana. </p>
<p><em><strong>Fulvio Franchi:</strong></em> Colleagues from South Africa and Finland then contacted us, providing precious information for localising the fragments. We immediately realised the importance of this event and mobilised the first search team.</p>
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<img alt="" src="https://images.theconversation.com/files/226966/original/file-20180710-70054-1n4j0zx.JPG?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">Meteorite fragment.</span>
<span class="attribution"><span class="source">Courtesy A. Proyer</span></span>
</figcaption>
</figure>
<p>The fragments of the asteroid 2018 LA – as it’s called – had scattered over a wide area in Botswana’s Central Kalahari Game Reserve, blown by the wind while falling down. Detailed calculations, by two independent groups, of the strewn field allowed our group of researchers to eventually find a fragment of the asteroid.</p>
<p><strong>What was the procedure for its retrieval and what were the challenges you faced?</strong></p>
<p><em><strong>Fulvio Franchi:</strong></em> There were a few factors to take into account when retrieving this meteorite in Botswana. </p>
<p>Firstly, you cannot just pick up a meteorite and own it –- at least not legally. Meteorites <a href="http://www1.eis.gov.bw/EIS/Policies/Environmental%20Policies/CAP%2059-03%20Monuments%20and%20Relics%20Act.pdf">are considered</a> relics by law and are to be handed over to the National Museum. </p>
<p>Secondly, the predicted fall area was in a National Park, the Central Kalahari Game Reserve. This required permits to enter as well as to work there. </p>
<p>Thirdly, the Botswana Geoscience Institute is the one mandated to act when unusual events like this happen. Naturally it’s been involved in the search.</p>
<p>The main technical challenges were to narrow down the search area. This was done by using eye-witness observations and video material, mainly from security cameras. Information on changes in direction and strength of winds, all the way from 27km above ground – where the meteorite exploded – to near-surface, was crucial. </p>
<p>The final challenge was going off-road, deep into the bush, walking for days in the territory of lions and elephants, snakes and scorpions. We had Park Rangers with rifles walking and camping with us, and fortunately the only casualties were a number of tyres being blown. An unexpected challenge was to have millions of other objects looking similar to a typically dark meteorite at first sight: pieces of burnt wood (from bushfires) or animal dung. But the excitement of finding something of scientific interest, and the joy of adventure, kept us going.</p>
<p><strong>Why is it important to study the meteorite?</strong></p>
<p><em><strong>Alexander Proyer:</strong></em> There are various, important reasons. </p>
<p>Each meteorite is a piece of the puzzle to understanding our solar system. The asteroids they are coming from represent different stages from dust to small bodies to planetesimals (small planets), that never made it to the final stage of a single planet. One could say that different stages towards the formation of full planets are preserved.</p>
<p>Some of them were shattered again by collision with other asteroids and now expose their interiors. Samples from such depths are unobtainable on Earth or any other intact planet. They are absolutely unique and help us understand the interior workings of Earth and other planets, which were built from very similar materials but are now strongly differentiated into a core, mantle and crust.</p>
<p>In terms of planetary defence, we now have a second case of remote observation of an asteroid linked to recovered material of it. If we ever need to defend ourselves against bigger asteroids in the future, it is vital to know what type of asteroid is coming in and its likelihood of disintegrating, at least partly, in the atmosphere or by being hit by of a defence-missile. By studying meteorites from asteroid 2018 LA it will be possible to link laboratory-determined meteorite properties to asteroid pre-impact remote observations. </p>
<p><em><strong>Fulvio Franchi:</strong></em> More detailed analyses, looking at the chemical composition of the rock and at the possible content of organic molecules, will also give us clues as to how life on earth was formed and, eventually, on the big question: is there any life out there?</p><img src="https://counter.theconversation.com/content/99678/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Each meteorite is a piece of the puzzle to understanding our solar system.Alexander Proyer, Professor of Petrology, Botswana International University of Science and Technology Fulvio Franchi, Senior lecturer, Botswana International University of Science and Technology Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/964312018-05-25T09:21:55Z2018-05-25T09:21:55ZHow we discovered 840 minor planets beyond Neptune – and what they can tell us<figure><img src="https://images.theconversation.com/files/218467/original/file-20180510-5968-7lw5y4.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">The Canada-France-Hawaii Telescope (CFHT) at sunset, which observed the OSSOS survey.</span> <span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Our solar system is a tiny but wonderfully familiar corner of the vast, dark universe – we have even been able to land spacecraft on our celestial neighbours. Yet its outer reaches are still remarkably unmapped. Now we <a href="https://ui.adsabs.harvard.edu/#abs/2018ApJS..236...18B/abstract">have discovered</a> 840 small worlds in the distant and hard-to-explore region beyond Neptune. This is the largest set of discoveries ever made, increasing the number of distant objects with well known paths around the sun by 50%.</p>
<p>These little icy worlds are important as they help us tell the solar system’s history. They can also help us <a href="https://theconversation.com/our-discovery-of-a-minor-planet-beyond-neptune-shows-there-might-not-be-a-planet-nine-after-all-75656">test the idea</a> that there’s a yet unseen planet lurking in the outer solar system. </p>
<p>Our planetary system as we see it today is not as it formed. When the sun was newborn, it was surrounded by a massive disk of material. Encounters with tiny, growing planets – including some of the worlds we’ve just discovered – moved the giant planets outward from the sun until they settled into their present locations. The growing planets, on the other hand, went everywhere, scattering both inward and outward. </p>
<p>Planetary migration also happened in far away systems around many other stars. Fortunately, the celestial bodies in our own planetary system are comparatively close by, making it the only place where we can see the intricate details of how migration happened. Mapping the minor planet populations that are left over from the disk lets us reconstruct the history of how the big planets were pushed into place.</p>
<h2>Mapping the sky</h2>
<p>The new discoveries were made as part of a five year project called the <a href="http://www.ossos-survey.org/">Outer Solar System Origins Survey</a> (OSSOS). The observations, conducted in 2013-2017, used the imaging camera of one of the world’s major telescopes – the <a href="http://www.cfht.hawaii.edu/">Canada-France-Hawaii Telescope</a> on Maunakea in Hawaii. The survey looked for faint, slow-moving points of light within eight big patches of sky near the plane of the planets and away from the dense star fields of the Milky Way. </p>
<p>With 840 discoveries made at distances between six and 83 astronomical units (au) – one such unit is the distance between the sun and the Earth – the survey gives us a very good overview of the many sorts of orbits these “trans-Neptunian objects” have.</p>
<p>Earlier surveys have suffered from losing some of their distant discoveries – when too few observations occur, the predicted path of a minor planet in the sky will be so uncertain that a telescope can’t spot it again, and it is considered “lost”. This happens more to objects with highly tilted and elongated orbits, producing a bias in what’s currently known about these populations.</p>
<p>Our new survey successfully tracked all its distant discoveries. The frequent snapshots we made of the 840 objects over several years meant that each little world’s orbit could be determined very precisely. In total, more than 37,000 hand-checked measurements of the hundreds of discoveries precisely pinned down their arcs across the sky.</p>
<p>We also created an accompanying software “simulator” (a computer model), which provides a powerful tool for testing the inventory and history of our solar system. This lets theorists <a href="https://arxiv.org/abs/1802.00460">test out their models</a> of how the solar system came to be in the shape we see it today, comparing them with our real discoveries.</p>
<h2>Strange new worlds</h2>
<p>The new icy and rocky objects fall into two main groups. One includes those that reside on roundish orbits in the Kuiper belt, which extends from 37au to approximately 50au from the sun. The other consists of worlds that orbit in a careful dance of avoidance with Neptune as it travels around the sun. These “resonant” trans-Neptunian objects, which include Pluto, were pushed into their current elongated orbits during Neptune’s migration outwards. </p>
<p>In the Kuiper belt, we found 436 small worlds. Their orbits confirm that a concentrated “kernel” of the population nestles on almost perfectly round, flat orbits at 43 to 45au. These quiet orbits may have been undisturbed since the dawn of the solar system, a leftover fraction of the original disk. Soon, we will see a member of this group up close: the <a href="https://theconversation.com/new-horizons-is-an-old-spacecraft-but-it-will-transform-our-knowledge-of-pluto-44524">New Horizons spacecraft</a>, which <a href="https://theconversation.com/new-horizons-finally-gets-up-close-with-pluto-for-15-minutes-44603">visited Pluto in 2015</a>, will be flying by a world that’s about the size of London on New Year’s Day 2019.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/218465/original/file-20180510-185500-4w73js.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">The dwarf planet candidate 2015 RR245 is on an exceptionally distant orbit, but is one of the few dwarf planets that could one day be reached by a spacecraft mission.</span>
<span class="attribution"><span class="source">Alex Parker/OSSOS</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We found 313 resonant trans-Neptunian objects, with the survey showing that they exist <a href="https://arxiv.org/abs/1802.05805">as far out as an incredible 130au</a> – and are <a href="https://arxiv.org/abs/1604.08177">far more abundant</a> than previously thought. Among these discoveries is the dwarf planet 2015 RR245, which is about half the size of Britain. It may have hopped onto its current orbit at 82au <a href="https://arxiv.org/abs/1607.06970">after an encounter with Neptune</a> hundreds of millions of years ago. It was once among the <a href="https://arxiv.org/abs/1803.07521">90,000 scattered objects</a> of smaller size that we estimate currently exist. </p>
<h2>Are there more planets?</h2>
<p>Among the most unusual of the discoveries are nine little worlds on incredibly distant orbits, never coming closer to the sun than Neptune’s orbit, and taking as long as 20,000 years to travel around our star. Their existence implies an unseen population of hundreds of thousands of trans-Neptunian objects on similar orbits.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/220427/original/file-20180525-51141-1jeqew.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">Artist’s concept of Planet Nine.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Robert Hurt</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>How these objects got on their present paths is unclear — some orbit so far out that, even at their closest approach, they are barely tugged by Neptune’s gravity. One explanation that has been put forward is that a yet unseen large planet, sometimes called “Planet Nine”, could be causing them to cluster in space. However, our nine minor planets all seem to be <a href="https://arxiv.org/abs/1706.05348">spread out smoothly</a>, rather than clustering. Perhaps the shepherding of such a large planet is more subtle – or these orbits instead <a href="https://theconversation.com/our-discovery-of-a-minor-planet-beyond-neptune-shows-there-might-not-be-a-planet-nine-after-all-75656">formed in a different way</a>.</p>
<p>The history of our solar system is just beginning to be told. We hope this new set of discoveries will help piece together the story.</p><img src="https://counter.theconversation.com/content/96431/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michele Bannister receives funding from the STFC, and has previously been funded by Canada&#39;s NRC and NSERC. She serves on the committee of the AAS&#39;s Division of Planetary Sciences.</span></em></p>Discovery of many icy worlds helps unravel the solar system's history.Michele Bannister, Research Fellow, planetary astronomy, Queen's University BelfastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/964102018-05-11T04:49:34Z2018-05-11T04:49:34ZA giant 'singing' cloud in space will help us to understand how star systems form<figure><img src="https://images.theconversation.com/files/218381/original/file-20180510-184630-8kvekt.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">The dark band is the Dark Doodad Nebula, a place where new stars and planets can form.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/cafuego/25910801567/">Flickr/cafuego</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We know that the birthplaces of stars are large molecular clouds of gas and dust found in space. </p>
<p>But what exactly determines the number and kind of stars and planets that are formed in these clouds? How was our Solar system nursed and how did it emerge from such a cloud billions of year ago?</p>
<p>These are mysteries that have been puzzling astronomers for decades, but research <a href="http://science.sciencemag.org/content/360/6389/635">published today in Science</a> adds an extra dimension to our understanding.</p>
<h2>A 3D approach</h2>
<p>Knowledge of the 3-dimensional structure of these clouds would be an important leap in our understanding of how stars and planets are born.</p>
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<strong>
Read more:
<a href="http://theconversation.com/from-pancakes-to-soccer-balls-new-study-shows-how-galaxies-change-shape-as-they-age-95379">From pancakes to soccer balls, new study shows how galaxies change shape as they age</a>
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<p>The physics responsible for the formation of stars is also responsible for shaping the clouds. But even with the most advanced telescopes in the world we can only see the two-dimensional projections of clouds on the plane of the sky.</p>
<p>Thankfully, there is a way around this problem. A recently discovered type of structure in molecular clouds, called striations, was found to form because of waves.</p>
<p>Here enters Musca, a molecular cloud that “sings”. Musca is an isolated cloud in the Southern sky, below the Southern Cross, that looks like a thin needle (see top image). It is hundreds of light years away and stretches about 27 light years across, with a depth of about 20 light years and width up to a fraction of a light year.</p>
<p>Musca is surrounded by ordered hair-like striations produced by trapped waves of gas and dust caused by the global vibrations of the cloud.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">3D model of Musca molecular cloud.</span>
<span class="attribution"><span class="source">Aris Tritsis, ANU</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Trapped waves act like a fingerprint – they are unique and can be used to identify the sizes of the boundaries that trapped them. Boundaries are naturally created at the edges of clouds where their physical properties change abruptly.</p>
<p>Just like a cello and a violin make very distinct sounds, clouds with different sizes and structures will vibrate in very different manners – they will “sing” different “songs”.</p>
<h2>A ‘song’ in the cloud</h2>
<p>By using this concept and calculating the frequencies seen in observations of Musca it was possible to measure for the first time the third dimension of the cloud, the one that extends along our line of sight.</p>
<p>The frequencies found in the observations were scaled to the frequency range of human hearing to produce the “song of Musca”.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/K9cp2FWHGLc?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">A “singing” molecular cloud.</span></figcaption>
</figure>
<p>The results from this method were amazing. Despite the fact that Musca looks like a thin cylinder from Earth, the true size of its hidden dimension is not small at all. In fact, it is comparable to its largest visible dimension on the plane of the sky.</p>
<p><img src="https://cdn.theconversation.com/static_files/files/108/tritsis2.gif?1526006594" width="100%"></p>
<h4>No longer a thin cylinder when the extra dimension is revealed (Aris Tritsis)</h4>
<p>Musca is not actively forming stars. It will be millions of years before gravity can overcome all opposing forces that support the cloud.</p>
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<em>
<strong>
Read more:
<a href="http://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away</a>
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<p>As a result, with its structure now determined, Musca can be used as a prototype laboratory against which we can compare our models and study the early stages of star formation.</p>
<p>We can use Musca to better constraint our numerical models and learn about our own Solar system. It could help solve many mysteries. For example, could the ices found in comets have formed in clouds rather than at a later time during the life of our solar system?</p><img src="https://counter.theconversation.com/content/96410/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aris Tritsis does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A three-dimensional look and listen at a dark cloud in space sheds new light on the mystery of how our solar system formed billions of years ago.Aris Tritsis, Postdoctoral Fellow, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/961082018-05-08T05:25:13Z2018-05-08T05:25:13ZThe latest from Juno as Jupiter appears bright in the night sky<figure><img src="https://images.theconversation.com/files/218016/original/file-20180508-46359-jrtpun.jpg?ixlib=rb-1.1.0&amp;rect=1036%2C0%2C2067%2C1264&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Time to peer below the swirling clouds of Jupiter.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA21974">NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Now is a great time to see Jupiter in the night sky, as the planet reaches opposition on Wednesday, May 9.</p>
<p>Opposition means that Jupiter sits opposite the Sun in the sky. So tonight, as the Sun sets in the west, Jupiter can be found rising in the east. It’s lovely and bright, outshining all the stars of the night sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218018/original/file-20180508-46347-1q0cjvz.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/218018/original/file-20180508-46347-1q0cjvz.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<p>In fact, opposition also means that Jupiter is at its closest to Earth, making the planet shine even more brilliantly than usual. So be sure to look east over the next few weeks to catch Jupiter at its best.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218019/original/file-20180508-46364-18ohfar.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/218019/original/file-20180508-46364-18ohfar.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Jupiter will be seen throughout May, rising in the east at sunset, ahead of the constellation Scorpius.</span>
<span class="attribution"><span class="source">Museums Victoria/stellarium</span></span>
</figcaption>
</figure>
<h2>Jupiter like we’ve never seen it before</h2>
<p>Also catching Jupiter at its best will be NASA’s spacecraft, <a href="https://www.missionjuno.swri.edu/">Juno</a>. After a five-year journey, Juno entered orbit around Jupiter in mid-2016. </p>
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<em>
<strong>
Read more:
<a href="http://theconversation.com/early-images-of-the-closest-look-at-jupiters-great-red-spot-80808">Early images of the closest look at Jupiter's Great Red Spot</a>
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<p>It’s the second spacecraft to orbit Jupiter (after <a href="https://www.jpl.nasa.gov/missions/galileo/">Galileo</a> in 1995), but importantly it’s the first to orbit Jupiter’s poles, allowing us to see a part of the planet that can’t be seen from Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/217983/original/file-20180507-46350-ib2s4u.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/217983/original/file-20180507-46350-ib2s4u.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">A new look at Jupiter, where multiple images have been combined to show the south pole in full sunlight.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles</span></span>
</figcaption>
</figure>
<p>Juno has shown us that Jupiter’s colourful bands – the clearly defined belts and zones (the dark and light bands, respectively) circling the bulk of the planet – give way to a striking configuration of cyclones at each of Jupiter’s poles. </p>
<p>Discovering cyclones at the top and bottom of Jupiter is not completely unexpected, but what’s surprising is their stability and the patterns they have formed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/217988/original/file-20180507-46335-cval8e.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/217988/original/file-20180507-46335-cval8e.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Jupiter’s northern cyclones in infrared, which captures the radiating heat. In this original image, darker regions are colder and cloudier, while brighter regions are relatively cloud-free, allowing us to look deeper.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM</span></span>
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<p>At the north pole, one central cyclone is surrounded by eight outer cyclones. In the south, the central cyclone has five others encircling it.</p>
<p>These cyclones are huge – the southern ones range from 5,600km to 7,000km in diameter; that’s about as <a href="https://solarsystem.nasa.gov/planets/mars/by-the-numbers/">wide as Mars</a>. The northern ones are slightly smaller, with diameters of around 4,000km to 4,600km. The wind speeds are as great as 350km per hour.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/217991/original/file-20180507-46359-1h7epum.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/217991/original/file-20180507-46359-1h7epum.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Jupiter’s southern cyclones. Note this enhanced image shows an inverted view, the darker regions are deep, while the higher, thicker clouds are white. This view aims to match the way we see clouds in space images of Earth.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM</span></span>
</figcaption>
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<p>Over the seven months of <a href="https://www.nature.com/articles/nature25491#f4">observations analysed so far</a>, the cyclones have remained surprisingly distinct, with no signs that they might merge together. Yet most of the cyclones are so tightly packed that their spiral arms are touching. (You can see the movement of the cyclones in this <a href="http://junocam.pictures/gerald/uploads/20170424/anim/jnc_pj05_N_089_to_105_blend4_enh.html">raw footage</a>.) </p>
<p>Also, the pattern itself is highly stable and shows barely any motion. Even though there’s a central cyclone churning around the pole, its motion doesn’t seem to be pushing the outer cyclones to circle around it (a la “Ring a Ring o’ Roses”). If they are circling the pole, then they must be drifting very slowly. </p>
<h2>Juno - please drive safely</h2>
<p>The other exciting thing about Juno is that it was built to probe the inner depths of Jupiter. One way it does this is by intricately <a href="https://www.nature.com/articles/nature25776">mapping Jupiter’s gravitational field</a> to a precision 100 times better than ever before.</p>
<p>Every 53 days, Juno carries out a stunning Jupiter flyby. The probe takes two hours to travel from one pole to the other, zipping past at more than 200,000km/h and skimming just 4,000km above Jupiter’s cloud tops.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/NsCirkzmfmk?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The latest Jupiter flyby (from April, 2018) shown in 70 seconds. NASA/JPL/SwRI/MSSS/SPICE/Gerald Eichstädt.</span></figcaption>
</figure>
<p>As Juno races by the planet it feels the gravitational tug of Jupiter. It speeds up slightly when flying over regions of high mass and slows down wherever the mass drops off. </p>
<p>These tiny changes in Juno’s speed are measured using a kind of interplanetary radar gun; Juno transmits a radio signal of a certain frequency and when it arrives here on Earth, any change to that frequency alerts us to Juno’s changing speed.</p>
<h2>Feeling the pressure</h2>
<p>If we think about Earth, there is a clear distinction between the clouds, the atmosphere, and the rocky planet itself. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218020/original/file-20180508-46341-1gd4s0b.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/218020/original/file-20180508-46341-1gd4s0b.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Swirling cloud belts of Jupiter’s northern hemisphere.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SwRI/MSSS/Kevin M Gill</span></span>
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</figure>
<p>But being made of gas, Jupiter is essentially all atmosphere. By definition, the planet begins when the atmospheric pressure of its gas equals 1 bar. That’s equivalent to the pressure we feel at sea level on Earth. </p>
<p>This provides a kind of surface for Jupiter, as such, although it is biased by our Earthling viewpoint. Juno is already giving us much better insights into how Jupiter is truly structured.</p>
<p>Previously what we’ve seen of Jupiter, the banded belts and zones, are the cloud tops sitting just above the planet’s “surface”. They circle around the planet, with alternate bands moving in opposite directions.</p>
<p>Juno’s data has shown that this banding <a href="https://www.nature.com/articles/nature25793">continues deep into Jupiter</a>, appearing to be much more than just a thin layer of weather (that’s driven by the Sun). </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rHwkdcppsuo?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Swirling clouds of Jupiter from Voyager 1 (1979). NASA/JPL/Björn Jónsson/Ian Regan.</span></figcaption>
</figure>
<h2>How low can you go?</h2>
<p>Juno’s gravity mapping was separated into two components: a static component, modelled as Jupiter’s gas rotating as one; and a dynamic component, arising from flows. </p>
<p>The dynamic component was revealed by a north-south asymmetry in Jupiter’s gravity field. What that means is that the way gravity varied from the equator up to the north pole was not consistent with how it changed from the equator down to the south pole.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218027/original/file-20180508-46356-cnfc64.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/218027/original/file-20180508-46356-cnfc64.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Jupiter is turbulent above and below.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran</span></span>
</figcaption>
</figure>
<p>It also became clear that these changes in gravity tracked the banded structure of Jupiter’s cloud layer. </p>
<p>As a result, the cloud tops must extend into Jupiter, becoming swirling jet streams that reach depths of 3,000km. The amount of mass swirling around was calculated to be 1% of Jupiter’s total mass – more than triple the mass of the Earth.</p>
<h2>Is there a ‘planet’ deep within?</h2>
<p>By analysing the <a href="https://www.nature.com/articles/nature25775">static component of Jupiter’s gravitational field</a>, it was found that there is a point where Jupiter’s gas starts to rotate in harmony, like a rigid sphere. </p>
<p>It sits below a wind depth of at least 2,000km but less than 3,500km, which is well consistent with the jet stream findings. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/launching-in-may-the-insight-mission-will-measure-marsquakes-to-explore-the-interior-of-mars-91080">Launching in May, the InSight mission will measure marsquakes to explore the interior of Mars</a>
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<p>At this depth, the pressure is 100,000 times greater than what we feel at the Earth’s surface and temperatures soar. Electric currents flowing through the compressed hydrogen gas and constrained by Jupiter’s powerful magnetic field, are thought to slow the winds down and drag the gas into uniform motion. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/LPvfeOiKbm8?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">First views of Jupiter’s magnetic dynamo shows irregularities and intense magnetic hot spots. NASA Goddard Space Flight Center.</span></figcaption>
</figure>
<p>As Juno continues to swing by Jupiter, scientists hope to better understand the <a href="https://www.nasa.gov/feature/jpl/nasa-s-juno-mission-provides-infrared-tour-of-jupiter-s-north-pole">dynamo powering Jupiter’s magnetic field</a> and ultimately to determine if Jupiter has a solid core, made of some kind of icy rock subjected to more than 50 million bars of pressure. Now that’s truly out of this world.</p><img src="https://counter.theconversation.com/content/96108/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Now's a great time to see Jupiter as it's about to be the closest to Earth for some time. Time too to catch up with the latest on the Juno mission, exploring the largest planet in our Solar System.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/951142018-04-20T09:46:05Z2018-04-20T09:46:05ZMysterious red spots on Mercury get names – but what are they?<figure><img src="https://images.theconversation.com/files/215058/original/file-20180416-587-gjlu39.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">MESSENGER enhanced colour image showing the southern half of Mercury&#39;s Caloris basin, hosting several red spots. </span> <span class="attribution"><a class="source" href="http://ode.rsl.wustl.edu/mercury/">NASA/JHUAPL/CIW</a>, <span class="license">Author provided</span></span></figcaption></figure><p>Mercury is the closest planet to the sun, but far from being a dull cinder of a world, it has instead <a href="https://theconversation.com/the-more-we-learn-about-mercury-the-weirder-it-seems-55972">turned out to be a real eye opener</a> for geologists. Among the revelations by <a href="https://www.nasa.gov/mission_pages/messenger/main/index.html">NASA’s MESSENGER probe</a>, which first flew past Mercury in 2008 and orbited it between 2011 and 2015, is the discovery of a hundred or so bright red spots scattered across the globe. Now they are at last being <a href="https://astrogeology.usgs.gov/news/nomenclature/names-approved-for-seven-faculae-on-mercury">named</a>.</p>
<p>Although they appear more yellow-orange than red on the accompanying colour-enhanced images, they are the reddest features on Mercury, a planet that looks dull and grey on unenhanced images. Most have 10-50km wide irregularly-shaped holes at their centres. Scientists soon interpreted the holes as volcanic vents and the spots as material thrown out by volcanic explosions. Explosive volcanism was not expected at Mercury, because formation of a planet close to the heat of the sun should have deprived it of the gaseous content necessary to power explosions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215199/original/file-20180417-164004-7a658e.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/215199/original/file-20180417-164004-7a658e.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Enhanced colour view showing a ‘red spot’ on Mercury now named Agwo Facula. The black and white image shows detail of the volcanic vent at the spot’s centre.</span>
<span class="attribution"><span class="source">NASA/JHUAPL/CIW</span></span>
</figcaption>
</figure>
<p>But MESSENGER revealed multiple lines of evidence showing that Mercury is actually quite rich in so-called “volatile components”. These include direct measurements of abundant sulphur, carbon, potassium and chlorine, and the discovery of patches of shallow <a href="https://www.space.com/28992-mercury-strange-hollows-messenger-photos.html">hollows</a> where it looks as if some unknown volatile material near the ground surface has been somehow dissipated into space.</p>
<p>Maybe this means that Mercury is actually the remains of an interloper from somewhere beyond the Earth’s orbit, where volatile material was available in greater amounts during planet formation. A <a href="https://www.astrobio.net/also-in-news/planet-mercury-result-early-hit-run-collisions/">“hit and run” impact</a> with the Earth or Venus in the early stages of their formation while Mercury was migrating inwards towards its present orbit close to the sun could have stripped it of much of its original rock, leaving the dense but volatile-rich body we see today.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215599/original/file-20180419-163978-cuklf0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/215599/original/file-20180419-163978-cuklf0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Three red spots, which were confusing to refer to until named. Nathair Facula at the top right is the largest. The smaller Neidr Facula lies 300km to the west, and Suge Facula lies 500km to the south. (Enhanced colour image)</span>
<span class="attribution"><span class="source">NASA/JHUAPL/CIW</span></span>
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<h2>Compound vents</h2>
<p>Whatever Mercury’s origin, the red spots and their source vents demonstrate explosive volcanic activity that in some cases likely continued into the most recent billion years of Mercury’s 4.5 billion year history. Scientists deduce this because some of the vents puncture young lava flows or the floors of young impact craters. </p>
<p>Overlapping structures within some vents show that they result from a succession of explosions at sites several kilometres apart. From this it can be inferred that each red spot is the accumulated product of several eruptions from its vent. </p>
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<figcaption><span class="caption">Volcanism, faults and hollows on Mercury.</span></figcaption>
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<p>Deciphering the relationships between explosive eruptions, lava flows, the growth of hollows and fault movements is among the major tasks for the <a href="https://theconversation.com/the-bepicolombo-spacecraft-is-ready-to-solve-the-many-mysteries-of-mercury-80687">forthcoming European-Japanese mission to Mercury, BepiColombo</a>, and is the kind of problem that excites planetary geologists.</p>
<h2>Snakes on a planet</h2>
<p>So why do the red spots need names, and how were the names decided? Names are needed for features on planets because it is cumbersome and unmemorable to refer to them merely by geographic coordinates. Names are allocated by <a href="https://planetarynames.wr.usgs.gov/">nomenclature working groups of the International Astronomical Union</a>, whose job is to achieve clarity and consistency, while also seeking fair representation of Earth’s many cultures. </p>
<p>Craters are given single word names, but names of most other features are in two parts: a specific name plus a descriptor term. The descriptor term is a word (usually of Latin origin) specifying what each type of feature looks like, but without implying that we know for certain how it formed. For example, we have “vallis” for valley, “planitia” for low plain, “planum” for high plain, and so on. The specific names used for each type of feature follow a convention adopted for each planet.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215063/original/file-20180416-540-1luurli.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/215063/original/file-20180416-540-1luurli.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">A cluster of overlapping red spots in the southeast of the Caloris basin, named collectively as Slang Faculae, using the Afrikaans word for snake. (Enhanced colour image)</span>
<span class="attribution"><span class="source">NASA/JHUAPL/CIW</span></span>
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<p>In the case of Mercury’s red spots, it is the spots themselves rather than the presumed volcanic vents at their centres that have been named. The chosen descriptor term is “facula”, which is already used for “bright spot” on various other planetary bodies. The theme chosen for the specific names of faculae on Mercury is the word “snake” in various languages. For example, the three faculae near <a href="https://www.nasa.gov/multimedia/imagegallery/image_feature_1697.html">Rachmaninoff crater</a> have been named Nathair Facula, Neidr Facula and Suge Facula, using “snake” in three minority European languages: Irish, Welsh and Basque. </p>
<p>Ten faculae in Mercury’s <a href="https://www.nasa.gov/image-feature/all-about-that-basin">Caloris basin</a> have so far been named each in a different African language. This means that scientists can now refer consistently to Agwo Facula (using the Igbo, southeastern Nigeria, word for snake) rather than “the spot around that kidney-shaped vent in the southwest of the Caloris basin”.</p>
<p>But why snake? Other than being a convenient way to draw names from all over the world, there does not have to be a reason for the choice of name. However, the Greek god Hermes and his Roman equivalent Mercury were <a href="https://en.wikipedia.org/wiki/Caduceus">traditionally portrayed bearing a staff entwined by two snakes</a>, so using snakes as a theme is a nice, incidental, nod to classical mythology.</p><img src="https://counter.theconversation.com/content/95114/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He has received funding from the UK Space Agency and the Science &amp; Technology Facilities Council for work related to Mercury and the European Space Agency&#39;s Mercury orbiter BepiColombo, and is currently funded by the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is co-leader of the European Space Agency&#39;s Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer). He is Educator on the Open University/FutureLearn Moons MOOC and chair of the Open University&#39;s Planetary Science and the Search for Life course.</span></em></p>Red spots suggest Mercury may have formed far away from the sun.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/892232017-12-18T05:07:51Z2017-12-18T05:07:51ZNo sign of alien life 'so far' on the mystery visitor from space, but we're still looking<figure><img src="https://images.theconversation.com/files/199615/original/file-20171218-17860-uinqud.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">An artist&#39;s impression of `Oumuamua, assuming it&#39;s a rock.</span> <span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1737a/">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The mystery object discovered earlier this year travelling through our Solar system is showing no signs of any alien life, despite plenty of efforts to look and listen for a signal.</p>
<p>Perhaps it’s ironic that the object should arrive in a year when we <a href="https://www.theverge.com/2017/12/16/16776506/arthur-c-clarke-author-science-fiction-books-century">celebrated the 100th anniversary</a> (on December 16) of the birth of science fiction author Arthur C Clarke.</p>
<p>One of his most popular novels, the award-winning <a href="https://www.goodreads.com/book/show/112537.Rendezvous_with_Rama">Rendezvous with Rama</a>, describes the high-speed entry of a cylindrical object into the Solar system. It’s initially thought to be an asteroid but a subsequent exploration reveals it to be an alien spaceship.</p>
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<em>
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Read more:
<a href="http://theconversation.com/a-fleeting-visit-an-asteroid-from-another-planetary-system-just-shot-past-earth-86482">A fleeting visit: an asteroid from another planetary system just shot past Earth</a>
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<h2>Exploring ‘Oumuamua</h2>
<p>Astronomers named our Solar system visitor 'Oumuamua, which is Hawaiian for “scout” or “messenger” as it was <a href="http://www.ifa.hawaii.edu/info/press-releases/interstellar/">fist detected by the University of Hawaii</a>’s Pan-STARRS1 telescope. </p>
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<a href="https://images.theconversation.com/files/192939/original/file-20171102-19883-6t4d6j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/192939/original/file-20171102-19883-6t4d6j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Tiny and very faint, this fast moving object (centre) was captured by astronomers as it passed through our Solar system.</span>
<span class="attribution"><a class="source" href="http://www.qub.ac.uk/News/Allnews/QueensUniversityastronomerscapturefirstvisitingobjectfromoutsideoursolarsystem.html">Queen's University Belfast</a></span>
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<p>From our distant exploration of 'Oumuamua we know it’s a red-brown, cigar-shaped object, about 400 metres long, and is moving so fast that it must have started its journey in some <a href="https://theconversation.com/a-fleeting-visit-an-asteroid-from-another-planetary-system-just-shot-past-earth-86482">distant stellar system</a>.</p>
<p>But we still have no idea what it is.</p>
<p>We know it’s not a comet, because it has no halo, and we know it’s not a normal asteroid, because we’ve never seen one that is so elongated – about ten times longer than it is wide. And its speed (about 100,000km per hour) rules out an origin within the Solar system or the <a href="https://solarsystem.nasa.gov/planets/oort/indepth">Oort cloud</a>, where comets come from.</p>
<h2>Aliens from another world?</h2>
<p>As scientists, we have to keep an open mind. For example, could it be an alien spacecraft? This might seem the stuff of comic-book fiction. Yet we know there are other <a href="https://exoplanets.nasa.gov/">Earth-like planets</a> out there, and some may host other civilisations. We must at least consider the possibility that it is an artificial object from one of these civilisations.</p>
<p>That would also be consistent with the cigar shape. We know that the <a href="http://www.popularmechanics.com/space/deep-space/a8140/what-would-a-starship-actually-look-like-12869471/">best shape for a large interstellar spacecraft</a> is not like the fictional <a href="http://www.startrek.com/database_article/enterprise">Starship Enterprise</a> of Star Trek fame, but more likely is elongated to minimise the damage from collisions with interstellar dust.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/199667/original/file-20171218-27557-7gq4o1.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/199667/original/file-20171218-27557-7gq4o1.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">The USS Enterprise is a great shape for a Christmas tree decoration, not so great shape for a real spacecraft.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/jdhancock/8395113234/">Flickr/JD Hancock</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The only problem with this idea is that this object is not gliding smoothly through our Solar system, but is tumbling head over heels, about once every eight hours. So if it is an alien spacecraft, it’s in trouble.</p>
<p>How can we tell what it is? The best way would be to get a good photo of it, but it is so far away that even the Hubble Space Telescope just sees a speck of reddish-brown light. And it is moving too fast to mount a space mission to get closer. Already it is starting to head out of the Solar system.</p>
<h2>Listening in for signals</h2>
<p>If it is an alien spacecraft, perhaps we might detect some radio signals from it. And if it’s in trouble, we might expect to hear a distress signal. Over the past few weeks, radio telescopes around the world have been straining to catch some whiff of radio emission. </p>
<p>The telescopes are well equipped for this job, as they are already engaged in the Search for Extra-terrestrial Intelligence (<a href="https://www.seti.org/">SETI</a>). The first serious SETI search was <a href="https://www.seti.org/seti-institute/project/details/early-seti-project-ozma-arecibo-message">made in 1960</a> by the radio astronomer <a href="https://www.seti.org/users/frank-drake">Frank Drake</a>, and SETI has continued on the world’s largest telescopes ever since.</p>
<p>The search continues methodically outwards from the Sun, with no detection so far, and yet SETI enthusiasts remain optimistic, pointing out that we have only searched a <a href="https://techcrunch.com/2016/02/04/seti-scientist-explains-why-we-havent-found-aliens-yet/">tiny fraction</a> of the stars in our galaxy. </p>
<p>The first search for signals from 'Oumuamua was by the SETI Institute, using the <a href="https://www.nbcnews.com/mach/science/mysterious-space-rock-actually-alien-spaceship-ncna829501">Allen Telescope Array</a>. They hoped they might detect some evidence of an artificial transmission - perhaps a series of pulses, or a narrow-bandwidth signal. But nothing was found. </p>
<p>A much larger search was made by the Breakthrough Foundation, which uses the Australian radio telescope (“The Dish”) operated by CSIRO at Parkes, New South Wales, and the Green Bank telescope in West Virginia, in the United States.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/woafGw2BAxk?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The passage of ‘Oumuamua through our Solar system.</span></figcaption>
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<p>Because 'Oumuamua is in the Northern sky, Green Bank can see it more easily than Parkes. Green Bank is still searching for signals from 'Oumuamua, but “so far” has <a href="https://breakthroughinitiatives.org/news/15">drawn a blank</a>.</p>
<p>All attempts so far to detect a signal have been unsuccessful. The observations are so sensitive that even a mobile phone on board 'Oumuamua would have been easily detected.</p>
<p>But so far, nothing. As 'Oumuamua heads back out into interstellar space, the attempts will wind down and the telescopes will return to their normal duties.</p>
<h2>So what is 'Oumuamua?</h2>
<p>One thing we know is that 'Oumuamua isn’t just a rock. It is the first interstellar object we’ve ever found in the Solar system, and its elongated shape means it is totally unlike a normal asteroid. </p>
<p>So it probably isn’t part of the natural process of planetary formation. The most likely explanation is that it is a giant shard of rock of unknown origin – perhaps debris from an interplanetary collision. </p>
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<em>
<strong>
Read more:
<a href="http://theconversation.com/what-is-the-search-for-extraterrestrial-intelligence-actually-looking-for-44977">What is the search for extraterrestrial intelligence actually looking for?</a>
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<p>But we cannot discount the possibility that it really is a spacecraft – perhaps one that got into trouble a long time ago and its corpse continues to tumble for eternity through the vastness of interstellar space.</p>
<p>Searches for signals from it will continue until it leaves us for ever, and perhaps something may still turn up. But the chances are that it will forever be a mystery. </p>
<p>What has changed is that we now know that such interstellar interlopers exist. <a href="https://arxiv.org/pdf/1711.05687.pdf">One estimate</a> is that there could be 10,000 such objects passing through the Solar system at any time. </p>
<p>If this is correct, then the hunt is on for more interstellar objects, and it won’t be long before we find another. Then we will see a new field of study open up as astronomers seek to understand their properties and origin. Will we find debris from planetary collisions? Or will we eventually find space junk from other civilisations and begin our own Rendezvous with Rama?</p><img src="https://counter.theconversation.com/content/89223/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ray Norris is a member of the SETI community and is a former chair of the SETI Post-detection committee.</span></em></p>Scientists looking for signs of alien life from the mystery object passing through our Solar system say they've found nothing "so far".Ray Norris, Professor, School of Computing, Engineering, & Maths, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/880442017-12-01T14:37:28Z2017-12-01T14:37:28ZMetal asteroid Psyche is all set for an early visit from NASA<figure><img src="https://images.theconversation.com/files/197280/original/file-20171201-10169-lmrzbl.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>Three times further away from the sun than the Earth lies an enormous lump of metal. Around 252km in diameter, the metallic “M-class” asteroid 16 Psyche is the target of NASA’s next mission to the belt of giant rocks that encircles the inner solar system. And the space agency now plans to visit it <a href="https://www.jpl.nasa.gov/news/news.php?feature=6854">much sooner</a> than originally planned.</p>
<p>Not only has the launch has been brought forward one year to the summer of 2022, but NASA’s scientists have also found a way to get to Psyche (pronounced SYKe-ee) much faster by taking a more efficient trajectory. The new route means the Psyche spacecraft won’t have to swing around the Earth to build up speed and won’t pass as close to the sun, so it needs less heat protection. It is now due to arrive in 2026, four years earlier than the original timeline.</p>
<p>The main aim of the journey to Psyshe is to gather more information about our own solar system. Psyche is one of many wandering members of the asteroid belt. Unlike the rest of its rocky neighbours, Psyche appears to be entirely made of nickel and iron, just like the Earth’s core. This, together with its size, has led to the theory that it might be the remains of the inside of a planet.</p>
<p>Asteroids are made up of <a href="https://www.astrobio.net/meteoritescomets-and-asteroids/primitive-particles/">primitive materials</a>, leftovers from the dust cloud from which our solar system originated. Different types of asteroids resemble the various steps it took to form planets from this dust cloud. This means they reveal a lot about the <a href="https://academic.oup.com/astrogeo/article/41/1/1.12/182262">origin and evolution of our solar system</a>. <a href="http://www.abc.net.au/news/science/2017-03-06/16-psyche-asteroid-like-no-other-metal-world-nasa-mission/8316054">Scientists think</a> Psyche could be what’s left of an exposed metal core of a planet very similar to Earth.</p>
<p>We actually derive much of our knowledge about asteroids and the evolution of planets from the <a href="https://www.meteorite.com/study-of-meteorites/">study of meteorites</a>. Many asteroids and comets are primitive <a href="https://socratic.org/questions/what-are-protoplanetary-bodies-and-what-do-they-do">protoplanetary bodies</a> accumulated from the same dust cloud our solar system originates from. As these protoplanetary bodies collide, gravity pulls them together into ever-larger bodies. Eventually these bodies become big and hot enough to partially melt, allowing heavy materials such as iron to sink to the core – and lighter material such as silicon to rise to the surface. </p>
<p>This process, known as <a href="https://www.windows2universe.org/glossary/differentiation.html">differentiation</a>, explains why Earth and other planets such as Mercury, Venus or Mars have an iron core and silicon-rich mantle and crust. The 16 Psyche asteroid is thought to be the leftover iron core of a planet stripped of its mantle in a giant collision.</p>
<p>But many questions regarding the formation of Psyche remain. How do you strip a planet of its mantle only leaving the core? Perhaps there is an alternative formation mechanism of an iron-rich body that does not involve differentiation? Psyche may once have been molten and, if so, did it cool from the inside out or from its surface to the core?</p>
<p>Also, <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/MagEarth.html">Earth’s magnetic field</a> comes from a liquid outer core circling around a solid inner core. Did these processes occur on Psyche and create a magnetic field? What elements other than iron accumulate in a core? And how does the surface geology of an iron body look compared to a rocky or icy body?</p>
<h2>Avoiding collisions</h2>
<p>There are other reasons for visiting asteroids. For one thing, possible collisions with Earth can have devastating effects. The impact of an 15km-wide <a href="http://large.stanford.edu/courses/2015/ph240/xu2/">asteroid approximately</a> 65m years ago is linked to the <a href="https://news.nationalgeographic.com/2016/06/what-happened-day-dinosaurs-died-chicxulub-drilling-asteroid-science/">extinction of the dinosaurs</a>. And the explosion of the 30m-diameter <a href="https://www.space.com/33623-chelyabinsk-meteor-wake-up-call-for-earth.html">Chelyabinsk asteroid</a> over Russia in 2013 led to injuries and damage on the ground. We need to know as much as possible about the composition and physical make-up of asteroids to devise the best ways to defend our planet.</p>
<p>Asteroids also provide resources. Those containing water or other valuable materials may act as stepping stones for human exploration of the solar system. And asteroids crossing Earth’s orbit may become convenient targets for mining operations, providing materials that are running out on Earth and potentially taking environmentally detrimental extraction methods off Earth. Companies including <a href="https://www.planetaryresources.com/">Planetary Resources</a> and countries like <a href="http://www.spaceresources.public.lu/en.html">Luxembourg</a> have already started to pursue these ideas in earnest.</p>
<p>The Psyche spacecraft will carry four instruments to gather as much information about the asteroid as it can: a camera, a <a href="https://mars.nasa.gov/odyssey/mission/instruments/grs/">gamma-ray spectrometer</a> to record what chemical elements are there, a magnetometer, and a radio gravity experiment. The data these devices collect should help us work out if Psyche is the frozen core of a former planet or simply a lump of unmelted metal. If it is a core, then it might help us determine exactly what’s at the centre of our own planet.</p>
<p>Lindy Elkins-Tanton, the lead scientist of the mission, probably summarised it best: <a href="https://www.nasa.gov/press-release/nasa-selects-two-missions-to-explore-the-early-solar-system">“We learn about inner space by visiting outer space”</a>.</p><img src="https://counter.theconversation.com/content/88044/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Schroeder receives funding from the UK Space Agency. </span></em></p>A new trajectory means the mission to uncover core facts about the asteroid belt will happen sooner than planned.Christian Schroeder, Senior Lecturer in Environmental Science and Planetary Exploration, University of StirlingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/878732017-11-21T12:46:08Z2017-11-21T12:46:08ZDiscovery of cigar-shaped asteroid from outer space could help unveil secrets of extrasolar worlds<figure><img src="https://images.theconversation.com/files/195568/original/file-20171121-18561-13rtjtx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Artist&#39;s impression of the enigmatic space rock.</span> <span class="attribution"><span class="source">ESO/M. Kornmesser</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It came from outer space … and went back there two weeks later, having astonished and excited astronomers and planetary scientists. A cigar-shaped object, less than half a kilometre long and barely bright enough to be detected by the world’s most powerful telescopes, payed us a flying visit in October this year – reminding us that the heavens still hold plenty of surprises.</p>
<p>There have been amazing changes in the way we view the smaller bodies in the solar system over the last five years. The Rosetta spacecraft’s observations of the duck-shaped comet 67P Churyumov-Gerasimenko <a href="https://theconversation.com/building-blocks-of-life-found-among-organic-compounds-on-comet-67p-what-philae-discoveries-mean-45379">taught us a lot</a>. Similarly, the heart-shaped ice-covered plains of Pluto <a href="https://theconversation.com/historic-close-ups-of-pluto-and-its-moon-charon-present-puzzle-for-scientists-44615">photographed by New Horizons</a> and the <a href="https://theconversation.com/ceres-reveals-its-salty-secrets-and-blurs-the-line-between-comets-and-asteroids-52105">bright spots on Ceres</a>, as imaged by the Dawn mission, have forced us to revise our ideas of the formation and evolution of comets, asteroids and faraway dwarf planets – and the relationship between them.</p>
<p>Now, courtesy, not of instruments on board spacecraft, but of detectors firmly based on the ground, we have observations of something that seems to be somewhere in the spectrum between comet and asteroid – but with a strange orbit that sets it apart from any other body in the solar system.</p>
<p>The orbit is hyperbolic, the object entered the solar system at a very steep angle to the ecliptic plane. It then rounded the sun, dipping below the ecliptic as it did so, and shot out again. What makes this orbit so interesting is that when its trajectory is traced back, it is clear that the object did not originate within the solar system – not even within the “Oort Cloud”, the reservoir that marks the outer fringes of our planetary system. </p>
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<img alt="" src="https://images.theconversation.com/files/195570/original/file-20171121-18555-1w5wzl8.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
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<span class="caption">The orbit of I1/2017U1.</span>
<span class="attribution"><span class="source">ESO/K. Meech et al.</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>The mystery visitor comes from beyond the fringe, and so is interstellar. This is the first time scientists have discovered an asteroid from outside the solar system, and the finding has been <a href="http://nature.com/articles/doi:10.1038/nature25020">published in Nature</a>.</p>
<h2>Window on extrasolar worlds</h2>
<p>In honour of this interstellar tourist – and perhaps in the hope that we might start to observe more of them, the <a href="https://www.iau.org/">International Astronomical Union</a> has come up with a new cataloguing system for interstellar asteroids. It is designated I1/2017U1, with the “I” for interstellar and “1” because it is the first. The interstellar object was detected by the <a href="https://www.ifa.hawaii.edu/research/Pan-STARRS.shtml">PanSTARRS1 telescope on Hawaii</a>, with follow-up observations on five other major telescopes. The discoverers of I1/2017U1 have named it “‘Oumuamua” – a Hawaiian-based word meaning a messenger reaching out from the distant past.</p>
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<img alt="" src="https://images.theconversation.com/files/195574/original/file-20171121-6031-p9ul49.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">PanSTARRS telescope.</span>
<span class="attribution"><a class="source" href="http://maxpixel.freegreatpicture.com/Telescopes-Observatory-Mauna-Kea-Hawaii-1567189">MaxPixel</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>'Oumuamua has an odd shape – about 800 metres long and ten times as long as it is wide. And although its hyperbolic orbit originally led observers to conclude that it was a comet, additional images showed no trace of a comet tail, and it was reclassified as an interstellar asteroid. It is likely comprised of rock and perhaps metals. Spectra, images of light captured from an object and spread out according to its wavelengths, reveal that its surface is reddish. This is the case for both some comets or a certain class of asteroids (D-class).</p>
<p>So, we have a small, dim, fast-moving object – why should we get excited? Let’s be grandiose about it – after all, practically every article following <a href="https://theconversation.com/experiments-simultaneously-detect-gravitational-waves-and-help-open-up-a-new-era-of-astronomy-84818">discovery of gravitational waves</a> declared that this was “opening a new window on the universe”. And, given its orbit, surely 'Oumuamua is worthy of similar hyperbole? I reckon we can say that the object is “illuminating the path to extrasolar worlds”, although we probably will not be able to trace exactly which planetary system it comes from. It shows that planetary systems around other stars are likely to have formed in a similar way to our own, ejecting fragments of rock like 'Oumuamua.</p>
<p>Planetary scientists study comets and asteroids because they are almost unchanged records of the material from which the solar system formed. Carbon-rich meteorites derived from certain asteroids contain organic matter that, when delivered to Earth by impact in the earliest days of terrestrial history, could have been the precursor material from which life developed. Such meteorites also contain small quantities of interstellar organics from reactions in the interstellar medium. </p>
<p>It is possible that 'Oumuamua and objects like it could carry similar records of their stellar formation. And it is also possible that there are many such objects hurtling through the solar system. As instruments on telescopes get more powerful, we will be able to detect them more readily and even make spectral measurements of their composition. This is exciting, as they almost certainly have different compositions than our own – shedding light on how the extrasolar system they came from formed.</p>
<p>As William Shakespeare <a href="http://nfs.sparknotes.com/hamlet/page_74.html">wrote over 400 years ago</a>: </p>
<blockquote>
<p>And therefore as a stranger give it welcome.<br>
There are more things in heaven and earth, Horatio,<br>
Than are dreamt of in your philosophy.</p>
</blockquote><img src="https://counter.theconversation.com/content/87873/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Monica Grady is a Fellow of the Natural History Museum and a Trustee of Lunar Mission One. She receives funding from the UK Space Agency, STFC and the Horizon 2020 program of the European Commission.</span></em></p>Having discovered an asteroid from outside the solar system for the first time, scientists are hoping there are more out there – illuminating the path to extrasolar worlds.Monica Grady, Professor of Planetary and Space Sciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/870112017-11-15T19:19:36Z2017-11-15T19:19:36ZWe've found an exo-planet with an extraordinarily eccentric orbit<figure><img src="https://images.theconversation.com/files/193903/original/file-20171109-14221-1d2ramr.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">An artist&#39;s impression of the exoplanet in close orbit to a star.</span> <span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/heic0807a/">ESA, NASA, G. Tinetti (University College London, UK &amp; ESA) and M. Kornmesser (ESA/Hubble)</a></span></figcaption></figure><p>The discovery of a planet with a highly elliptical orbit around an ancient star could help us understand more about how planetary systems form and evolve over time.</p>
<p>The new planet, HD76920b, is four times the mass of Jupiter, and can be found some 587 light years away in the southern constellation Volans, the Flying Fish. At its closest it skims the surface of its host star, HD76920. At its furthest, it orbits almost twice as far from its star as Earth does from the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/193771/original/file-20171108-27001-la83tj.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Superimposing HD76920b’s orbit on the Solar system shows how peculiar it is. Its orbit is more like that of the asteroid Phaethon than any of the Solar system’s planets.</span>
<span class="attribution"><span class="source">Jake Clark</span></span>
</figcaption>
</figure>
<p>Details of the planet and its discovery are <a href="http://arxiv.org/abs/1711.05378">published today</a>. So how does this fit into the planet formation narrative, and are planets like it common in the cosmos?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/a-fleeting-visit-an-asteroid-from-another-planetary-system-just-shot-past-earth-86482">A fleeting visit: an asteroid from another planetary system just shot past Earth</a>
</strong>
</em>
</p>
<hr>
<h2>The Solar system</h2>
<p>Before the first exoplanet discovery, our understanding of how planetary systems formed came from the only example we had at the time: <a href="https://solarsystem.nasa.gov/planets/">our Solar system</a>.</p>
<p>Close to the Sun orbit four rocky planets – Mercury, Venus, Earth and Mars. Further out are four giants – Jupiter, Saturn, Uranus and Neptune. </p>
<p>Scattered in their midst we have debris – <a href="http://cometography.com/">comets</a>, <a href="https://solarsystem.nasa.gov/planets/asteroids">asteroids</a> and the <a href="https://theconversation.com/planet-or-dwarf-planet-all-worlds-are-worth-investigating-74682">dwarf planets</a>.</p>
<p>The eight planets move in almost circular orbits, close to the same plane. The bulk of the debris also lies close to that plane, although on orbits that are somewhat more eccentric and inclined.</p>
<p>How did this system form? The idea was that it coalesced from a disk of material surrounding the embyronic Sun. The colder outer reaches were rich in ices, while the hotter inner regions contained just dust and gas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/194299/original/file-20171113-27579-1t07ti9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The Solar system formed from a protoplanetary disk, surrounding the young Sun.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>Over millions of years, the tiny particles of dust and ice collided with one another, slowly building ever larger objects. In the icy depths of space, the giant planets grew rapidly. In the hot, rocky interior, growth was slower. </p>
<p>Eventually, the Sun blew away the gas and dust leaving a (relatively) orderly system – roughly co-planar planets, moving on near-circular orbits.</p>
<h2>The exoplanet era</h2>
<p>The first exoplanets, discovered in the 1990s, shattered this simple model of planet formation. We quickly learned that they are <a href="https://www.nasa.gov/feature/jpl/20-intriguing-exoplanets">far more diverse</a> than we could have possibly imagined.</p>
<p>Some systems feature giant planets, larger than Jupiter, <a href="https://theconversation.com/its-all-in-the-rotation-exploring-planets-orbiting-distant-stars-59593">orbiting incredibly close to their star</a>. Others host eccentric, solitary worlds, with no companions to call their own. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/193775/original/file-20171108-26968-fbdoei.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Artist’s impression of the Hot Jupiter HD209458b - a planet so close to its star that its atmosphere is evaporating to space.</span>
<span class="attribution"><span class="source">European Space Agency, A.Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS, France) and NASA</span></span>
</figcaption>
</figure>
<p>This wealth of data reveals one thing – planet formation and evolution is <a href="https://theconversation.com/from-dust-clouds-to-wobbly-orbits-for-new-planets-29704">more complicated and diverse than we ever imagined</a>.</p>
<h2>Core accretion vs dynamical instability</h2>
<p>As a result of these discoveries, astronomers developed two competing models for planet formation. </p>
<p>The first is <a href="https://blog.planethunters.org/tag/core-accretion/">core accretion</a>, where planets form gradually, through collisions between grains of dust and ice. The theory has grown out of our old models of Solar system formation. </p>
<p>The competing theory is dynamical instability. Once again, the story begins with a disk of material around a youthful star. But that disk is more massive, and becomes unstable under its own self-gravity, causing clumps to grow. These clumps rapidly form planets, in thousands of years.</p>
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<figcaption><span class="caption">Massive protoplanetary disks can become unstable, rapidly giving birth to giant planets.</span></figcaption>
</figure>
<p>Both models can explain some, but not all, of the newly discovered planets. Depending on the initial conditions around the star, it seems that both processes can occur. </p>
<p>Each theory offers potential to explain eccentric worlds in somewhat different ways.</p>
<h2>How do you get an eccentric planet?</h2>
<p>In the dynamical instability model you can easily get several clumps forming and interacting, slinging one another around until their orbits are both tilted and eccentric. </p>
<p>Under the core accretion model things are a bit harder, as this method naturally creates co-planar, ordered planetary systems. But over time those systems can become unstable.</p>
<p>One possible outcome is for one planet to eject the others through a series of chaotic encounters. That would naturally leave it as a solitary body, following a highly elongated orbit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/194290/original/file-20171113-27573-s6akrq.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Chaotic planetary systems can eject planets entirely, leading to lonely rouge planets.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>But there is another option. <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/binary_intro.htmlhttp://www.atnf.csiro.au/outreach/education/senior/astrophysics/binary_intro.html">Many stars in our galaxy are binary</a> – they have stellar companions. The interactions between a planet and its host star’s sibling could readily stir it up and eventually eject it, or place it on an extreme orbit.</p>
<h2>An eccentric planet</h2>
<p>This brings us to our newly discovered world, HD76920b. A handful of similarly eccentric worlds have been found before, but HD76920b is unique. It orbits an ancient star, more than two billion years older than the Sun.</p>
<p>The orbit HD76920b is following is not tenable in the long-term. As it swings close to its host star, it will experience dramatic tides. </p>
<p>A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity. Those tides will be far greater than any we experience on Earth.</p>
<p>That tidal interaction will act over time to circularise the planet’s orbit. The point of closest approach to the star will remain unchanged, but the most distant point will gradually be dragged closer in, driving the orbit towards circularity.</p>
<p>All of this suggests that HD76920b cannot have occupied its current orbit since its birth. If that were the case, the orbit would have circularised aeons ago.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/194298/original/file-20171113-27573-1dmbb6a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Extremely eccentric planets have been discovered before, but this is the first around such an ancient star.</span>
<span class="attribution"><span class="source">Goddard Space Flight Center/NASA</span></span>
</figcaption>
</figure>
<p>Perhaps what we’re seeing is evidence of a planetary system gone rogue. A system that once contained several planets on circular (or near circular) orbits. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/exoplanet-discovery-by-an-amateur-astronomer-shows-the-power-of-citizen-science-75912">Exoplanet discovery by an amateur astronomer shows the power of citizen science</a>
</strong>
</em>
</p>
<hr>
<p>Over time, those planets nudged one another around, eventually hitting a chaotic architecture as their star evolved. The result – chaos – with most planets scattered and flung to the depths of space leaving just one – HD76920b.</p>
<p>The truth is, we just don’t know – yet. As is always the case in astronomy, more observations are needed to truly understand the life story of this peculiar planet.</p>
<p>One thing we do know is the story is coming to a fiery end. In the next few million years, the star will swell, devouring its final planet. Then, HD76920b will be no more.</p><img src="https://counter.theconversation.com/content/87011/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p><p class="fine-print"><em><span>Rob Wittenmyer receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Stephen Kane receives funding from NASA.</span></em></p>A solitary planet in an eccentric orbit around an ancient star may help astronomers understand exactly how such planetary systems are formed.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandJake Clark, PhD Student, University of Southern QueenslandRob Wittenmyer, Associate Professor (Astrophysics), University of Southern QueenslandStephen Kane, Associate Professor, University of California, RiversideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/868362017-11-06T23:12:43Z2017-11-06T23:12:43ZHow scientists discovered our first interstellar mystery visitor<figure><img src="https://images.theconversation.com/files/193265/original/file-20171103-1027-nyw8bb.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">It’s a bird… It’s a plane… No, it&#39;s an object from another solar system! Astronomers have been scrambling to identify a mysterious object passing through our solar system at a speed of about 160,000 km/h. This NASA file image shows a simulation of asteroids passing the earth.</span> <span class="attribution"><span class="source">(Handout)</span></span></figcaption></figure><p>The astronomy world has been abuzz recently with the discovery of a new object cutting through our solar system. Its path indicates it came from interstellar space — the first body of its kind ever observed.</p>
<p>When it was first discovered, <a href="http://www.minorplanetcenter.net/mpec/K17/K17UI1.html">astronomers thought this object was a comet and gave it the name C/2017 U1,</a> but further observations revealed the fast-moving object did not have a tail of dust and gas as comets do. Instead, its image was seen as slightly extended due to its rapid motion across the sky.</p>
<p>Within hours of the discovery being announced in the early morning of Oct. 25, the world’s astronomers began to train their facilities on this unusual object. </p>
<p>I’m an astronomer with the National Research Council of Canada, a leader of the <a href="http://www.ossos-survey.org">Outer Solar System Origins Survey (OSSOS)</a> and member of the <a href="https://www.colossos.net">Colours for OSSOS (ColOSSOS)</a> project that is measuring the surface colours of Kuiper belt objects discovered in <a href="http://www.ossos-survey.org">OSSOS</a>. The <a href="https://www.colossos.net">ColOSSOS</a> team immediately began observing this unusual visitor.</p>
<h2>What is this thing?</h2>
<p>The initial discovery announcement includes information from 10 observatories, each with its own team of astronomers. These observatories would have been privately alerted to the existence of this unusual detection and asked to provide confirming observations. This is a common practice to avoid a false announcement of an object’s discovery when the orbit is significantly different than expectations.</p>
<p>The International Astronomical Union designated the the object A/2017 U1. It’s not the most romantic name conceivable but fascinating nonetheless.</p>
<p>The name A/2017 U1 is a code describing the object. A for asteroid, followed by the year, bi-weekly period U (astronomers break the year into 26 two-week periods) and the number 1 to indicate this is the first object in this class in 2017. </p>
<p>In reality, however, this is the first-ever known interstellar asteroid that humans have directly observed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193469/original/file-20171106-1046-1frru7h.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/193469/original/file-20171106-1046-1frru7h.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">A/2017 U1 is probably of interstellar origin. This NASA Jet Propulsion Laboratory/Caltech diagram shows its path of travel from above the plane of our solar system, around the sun and past earth at 44 kilometres per second. It was closest to the sun on Sept. 9.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/jpl/small-asteroid-or-comet-visits-from-beyond-the-solar-system">(Handout)</a></span>
</figcaption>
</figure>
<h2>Asteroids</h2>
<p>From early in the process of the formation of planetary systems there is a rather large surplus of material — debris — that remains, which is not taken up into major planets. </p>
<p>In our solar system, the asteroid belt is the nearest accessible remnant of such debris. The asteroid that killed the dinosaurs likely came from this belt of material.</p>
<p>But the asteroid belt is a tiny fraction of the debris that a typical planetary system produces. Looking out at nearby stars that appear to be forming planetary systems, such as Epislon Eridani, <a href="https://doi.org/10.1093/mnras/stx1072">we can see rings of billions of particles of debris</a>. These rings of dusty debris are themselves only remnants of the initial material.</p>
<p>Why so much debris? Once planets form, chaos takes over. Giant planets push and pull on each other with their massive gravity, scattering each other about and ejecting billions of smaller objects — some as large as thousands of kilometres across — into the depths of space. </p>
<p>In our solar system, some of the material forms a halo of objects orbiting the sun at distances of 10,000 to 100,000 astronomical units (the Oort Cloud). An astronomical unit is the average distance between the sun and earth — about 149,597,870 kilometres — which is the standard unit of measure in planetary science. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/53Js-_vo3mo?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">NASA describes how near-earth asteroids are detected. (NASA)</span></figcaption>
</figure>
<p>The physics of planet formation indicates that many billions of small objects — up to a few kilometres across — are formed for every object the size of Pluto. Some scientists argue that the large objects accrete from dust sizes and up, while others contend that large objects — 100 kilometres across or more — form in single events and then grind down to smaller pieces.</p>
<p>Regardless, these small objects can be held in very distant orbits or ejected from the influence of a star’s gravity entirely. Once ejected, they become free-floating planetary mass objects, drifting through our galaxy — if you can call 80,000 km/h drifting. </p>
<p>The <a href="https://www.nature.com/articles/nature10092">existence of free floating planets</a> that formed in orbit around a star and were then ejected has long been discussed and provided the first direct evidence for the existence of such planetary mass objects floating through space.</p>
<p>Given models of planet formation, astronomers understood that many <a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa5c8a/pdf">asteroid-sized objects should be freely floating</a> also, but would they ever be detected? Most agreed that was unlikely, but not impossible.</p>
<h2>Discovering A/2017 U1 and its origins</h2>
<p>The <a href="https://panstarrs.stsci.edu/">Panoramic Survey Telescope and Rapid Response System (PanSTARRS)</a> survey of the sky is designed to discover and track objects that might be on a collision course with the Earth. PanSTARRS surveys the entire sky every few nights and has discovered thousands of asteroids, near and far, in our solar system.</p>
<p>One part of the mission is to alert supporting facilities, and the population of Earth, if an object with a high likelihood of Earth impact is detected. The massive data volumes produced by PanSTARRS are searched every morning and alerts to new and interesting discoveries are sent out to the world community. It is because of this machinery that astronomers were alerted to the existence of A/2017 U1.</p>
<p><a href="https://twitter.com/joemasiero">Dr. Joe Masiero </a>of NASA’s Jet Propulsion Laboratory had the 200-inch (5-metre) Hale telescope at Mount Palomar observatory in California trained on the object within hours of the public announcement after being <a href="https://twitter.com/astrokiwi/status/923061590706085891">alerted over Twitter</a>. Two days later, the initial <a href="https://arxiv.org/abs/1710.09977v1">draft of an article describing his observations</a> was online. These initial measurements are quite rough and the weather did not cooperate, but they show that the object is red in colour, much like members of the <a href="https://solarsystem.nasa.gov/planets/kbos">Kuiper belt</a> — and unlike the much closer asteroid belt. </p>
<p>These facts, along with the asteroid’s trajectory, suggest it is of interstellar origin.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/193320/original/file-20171105-1041-164hrly.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/193320/original/file-20171105-1041-164hrly.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">A/2017 U1 is seen as a white dot near the middle of this 300-second false-colour image taken on Oct. 29 from Gemini Observatory on Mauna Kea, Hawaii, with stars as streaks, and the night sky in orange.</span>
<span class="attribution"><span class="source">(Gemini Observatory, NSF, AURA /M. T. Bannister, R. E. Pike, M. E. Schwamb)</span></span>
</figcaption>
</figure>
<p>More details of the properties of this visitor will be analyzed in the coming days. The <a href="https://www.colossos.net">ColOSSOS</a> group obtained observations of the object with the Gemini eight-metre telescope in Hawaii a few days ago. Details of those observations, along with those from other groups, will soon be <a href="https://arxiv.org/find/all/1/abs:+EXACT+a%252F2017_u1/0/1/0/all/0/1">published on arxiv.org</a>. </p>
<p>One thing we are left to contemplate is the home from which this object made its journey to our region of space. The trajectory excludes the possibility that this object is from our solar system. This is a visitor from another star — a natural interstellar spaceship. </p>
<p><a href="https://twitter.com/ericmamajek">Eric Mamajek</a>, deputy program schief scientist at NASA’s <a href="https://exoplanets.nasa.gov/exep/">Exoplanet Exploration Program,</a> reports that A/2017 U1’s motion velocity relative to the galactic centre makes stars in the group with <a href="https://arxiv.org/abs/1710.11364">Epsilon Eridani a plausible origin</a>. If e-Eri was its home, then the object has come from just 10.5 light-years away, a journey of about 120,000 thousand years given its current speed — a mere blink in time.</p>
<p>A/2017 U1 is a visitor from another world. The question that remains: As with Arthur C. Clarke’s visitors, do they <a href="https://www.goodreads.com/quotes/1106902-and-on-far-off-earth-dr-carlisle-perera-had-as-yet">come in threes?</a></p><img src="https://counter.theconversation.com/content/86836/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>JJ Kavelaars receives funding from the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation and the US National Aeronautics and Space Administration.</span></em></p>Astronomers have detected what is believed to be the first interstellar object ever seen passing through our solar system.JJ Kavelaars, Senior Research Officer in Astronomy, University of VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/864822017-11-05T19:17:19Z2017-11-05T19:17:19ZA fleeting visit: an asteroid from another planetary system just shot past Earth<figure><img src="https://images.theconversation.com/files/192939/original/file-20171102-19883-6t4d6j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Tiny and very faint, this fast moving object (centre) was captured by astronomers as it passed through our Solar system.</span> <span class="attribution"><a class="source" href="http://www.qub.ac.uk/News/Allnews/QueensUniversityastronomerscapturefirstvisitingobjectfromoutsideoursolarsystem.html">Queen&#39;s University Belfast</a></span></figcaption></figure><p>The discovery of <a href="https://www.nasa.gov/feature/jpl/small-asteroid-or-comet-visits-from-beyond-the-solar-system">an unusual small object</a> in the Solar system last month caught the imagination of the global astronomical community. Scientists around the world were asking “what is it?” and “where did it come from?”</p>
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<p>Within days, they realised this tiny body was moving very quickly, and <a href="http://www.minorplanetcenter.net/mpec/K17/K17UI1.html">might not be bound to our Solar System</a>. Astronomers swung telescopes towards the faint object, and soon confirmed it as the first interstellar object ever observed passing through the Solar system.</p>
<p>So will there be more of these celestial vagabonds? To answer that question, we must first take a close look at our own Solar system. </p>
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Read more:
<a href="http://theconversation.com/water-water-everywhere-in-our-solar-system-but-what-does-that-mean-for-life-76315">Water, water, everywhere in our Solar system but what does that mean for life?</a>
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<h2>Comets and asteroids - leftovers of creation</h2>
<p>The Solar system includes debris left behind <a href="https://theconversation.com/giant-impacts-planet-formation-and-the-search-for-life-elsewhere-33478">from its formation</a>. The bulk of that material is trapped in regions where objects remain relatively unperturbed on timescales of billions of years. </p>
<p>Between the orbits of Mars and Jupiter lurk <a href="https://www.space.com/16105-asteroid-belt.html">millions of asteroids</a>, the relics of planet formation. Beyond the orbit of Neptune are <a href="https://solarsystem.nasa.gov/planets/kbos/indepth">the trans-Neptunian objects</a> - millions of icy bodies, held in cold storage. Finally, stretching halfway to the nearest star, is <a href="https://solarsystem.nasa.gov/planets/oort/indepth">the Oort cloud</a>, thought to contain more than ten trillion cometary nuclei.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/192942/original/file-20171102-26426-crjn71.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/192942/original/file-20171102-26426-crjn71.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">The regions of our Solar system (not to scale).</span>
<span class="attribution"><span class="source">Shutterstock/hydra viridis</span></span>
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</figure>
<p>Most of these objects will remain in these regions forevermore. But over time a small fraction will be shaken loose, injected to orbits that are far less stable.</p>
<p>They then live brief, chaotic lives. Flung around the Solar system as a result of the gravitational influence of the planets, they can end up on orbits that bring them close to Earth and the Sun. </p>
<p>Some <a href="https://www.nasa.gov/feature/goddard/2016/hubble-takes-close-up-look-at-disintegrating-comet">will fall apart</a>, while others <a href="https://www.scientificamerican.com/article/s19-the-comet-that-battered-jupiter-and-shook-congress/">will crash into one of the planets</a>. The majority will eventually leave the Solar system, never to return. Such ejections are far from a new phenomenon as the Solar system has been shedding debris since it formed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/192965/original/file-20171102-26462-i4l5i.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/192965/original/file-20171102-26462-i4l5i.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">In 1994, fragments of comet Shoemaker-Levy 9 collided with Jupiter, leaving scars the size of the Earth.</span>
<span class="attribution"><span class="source">Hubble Space Telescope Comet Team and NASA</span></span>
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<h2>The Solar system is not unique</h2>
<p>Over the past 20 years, we have learned that the majority of stars are accompanied by planets and their attendant debris. Observing stars at infrared wavelengths, we have learned that many are also accompanied by <a href="https://theconversation.com/comet-families-similar-to-our-own-are-found-around-another-star-32817">far greater quantities of debris than we see in the Solar system</a>. </p>
<p>We therefore move in a galaxy full of stars that are shedding debris to the depths of space. The void between the stars is far from empty.</p>
<p>With so much material floating freely in space, it was always likely that some of that debris would swing close enough to the Sun for us to detect it – which brings us back to our newly discovered object.</p>
<h2>Our first interstellar vagabond</h2>
<p>When the new object was first detected, it was apparent that it was moving on a highly elongated orbit. For that reason, scientists assumed it was a long-period comet, and named it <a href="http://www.minorplanetcenter.net/mpec/K17/K17UI1.html">C/2017 U1 Pan-STARRS</a>.</p>
<p>As more observations were made, the only way that scientists could fit the object’s orbit to the data was if it was moving on a hyperbolic orbit – in other words, if it was not gravitationally bound to the Solar system.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/woafGw2BAxk?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Animation showing the orbit of the interstellar asteroid A/2017 U1.</span></figcaption>
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<p>Over the days that followed the object’s discovery, detailed observations revealed no evidence of any cometary activity. Long exposures using the world’s largest telescopes showed nothing more than a fast moving speck of light. </p>
<p>Rather than a comet, the object seems asteroidal, which suggests it formed relatively close to its parent star. As a result, it was renamed A/2017 U1 – the first time in history that an object has been reclassified as being solely an asteroid rather than a comet.</p>
<h2>But where did it come from?</h2>
<p>Now we have a better handle on how A/2017 U1 is moving, people have begun to speculate on its origin. </p>
<p>Tracking its orbit back in time is no easy task. The further back we look, the less precisely we can say exactly where the object was. </p>
<p>What we can say is that A/2017 U1 approached the Solar system from roughly the direction of <a href="https://www.space.com/21719-vega.html">the bright northern star Vega</a>. We know the inbound direction to about one-fifth of a degree, and the path lies around five degrees from that star in the northern sky.</p>
<p>Unfortunately, we can’t go from this to tying A/2017 U1’s origin to any given star. To do that we would need to know the motions of every single star with exquisite precision, as well as how they affect one another (and our object).</p>
<p>But what we can say is that the asteroid originates from a star within our own galaxy. Were it an intergalactic guest, it would be travelling much faster.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/192940/original/file-20171102-19883-g75n2b.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/192940/original/file-20171102-19883-g75n2b.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">The path of A/2017 U1 (dashed line) as it crossed the plane of the planets in our Solar system and then turned and headed back out.</span>
<span class="attribution"><a class="source" href="http://www.ifa.hawaii.edu/info/press-releases/interstellar/">Brooks Bays/SOEST Publication Services/UH Institute for Astronomy</a></span>
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<h2>The future</h2>
<p>What do we learn from A/2017 U1’s fleeting visit? The most important result is the confirmation of a long held expectation – that we would eventually discover comets and asteroids from distant stars sleeting through our Solar system.</p>
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Read more:
<a href="http://theconversation.com/say-hello-to-the-earths-nearest-exoplanet-neighbour-proxima-centauri-b-64351">Say hello to the Earth's nearest exoplanet neighbour: Proxima Centauri b</a>
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<p>In coming years, new surveys will vastly increase our chances of finding further visitors. Eventually, such discoveries will be commonplace, and we will learn how many objects like A/2017 U1 are scattered through the galaxy. This will provide a wealth of information on how planetary systems form and evolve. </p>
<p>If we detect such objects with enough warning, more detailed observations could examine their chemical and isotopic compositions, allowing us to sample the makeup of planetary systems far from our own. The possibilities are endless, and hugely exciting!</p>
<p>But what of A/2017 U1’s fate? Its days near the Sun are over, and it is rapidly heading back to the cold depths of interstellar space. </p>
<p>In millions or billions of years, it might swing past another star, and visit alien worlds - but most likely it will continue to drift forevermore, cold and dark, through the spaces between the stars.</p><img src="https://counter.theconversation.com/content/86482/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The mystery object seen moving through our Solar system shows the void between the stars is far from empty. So can we expect more interstellar visitors?Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/850452017-10-04T08:38:18Z2017-10-04T08:38:18ZMonster volcanoes on Mars: how space rocks are helping us solve their mysteries<figure><img src="https://images.theconversation.com/files/188620/original/file-20171003-18673-1bpti6e.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Olympus Mons, biggest volcano in the Solar System. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/132160802@N06/31715862641">Justin Cowart</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Mars famously has the largest volcanoes known to science. The largest is Olympus Mons, pictured above, which towers 22km above the surrounding plains – over two and a half times taller than Mount Everest. This extinct volcano is 640km wide even at its narrowest point, greater than the distance between London and Glasgow, or Los Angeles and San Francisco. And Olympus Mons isn’t alone in the Earth-beating stakes – three other Martian volcanoes are more than 10km high.</p>
<p>Mars is a small world. It is half the diameter and less than 11% the mass of Earth, so the existence of such volcanoes was particularly surprising when they were revealed by the first satellite orbiter pictures <a href="https://history.nasa.gov/SP-441/ch5.htm">collected by</a> NASA in the 1970s. Ever since, scientists have been keen to discover more about these towering mountains – what they are made of, when they first erupted, when they were last active, and why they grew so much larger than anything on our own planet. So how are we getting on?</p>
<p>Spacecraft have sent back stunning images and data about these volcanoes over the years, yielding an amazing amount of knowledge. We have learned a lot from the impact craters made by asteroids, for example, since older areas on the planet have more craters than younger areas. </p>
<p>From this, scientists have <a href="https://websites.pmc.ucsc.edu/%7Ercoe/eart290C/Additional%20Papers/Werner_MarsVolcanicHistory_Icarus09.pdf">concluded that</a> the volcanoes on Mars began erupting well over 3.5 billion years ago, roughly comparable to how far back eruptions go on Earth. The most recent Martian eruptions <a href="https://www.nasa.gov/feature/goddard/2017/mars-volcano-earths-dinosaurs-went-extinct-about-the-same-time">are perhaps</a> a few tens of millions of years old. No active volcanoes have been discovered; at least not yet.</p>
<h2>Rock recording</h2>
<p>Scientists also study Martian volcanoes by examining <a href="https://theconversation.com/heres-the-blueprint-for-a-global-fireball-observatory-and-why-we-need-one-82798">certain meteorites</a> on Earth. Asteroid strikes on Mars are relevant to this as well, since massive amounts of energy are released when big asteroids hit the surface. This is often sufficient to blast other pieces of rock upwards, some of which reach Earth as meteorites. </p>
<p>We have now recovered over 100 samples of genuine Martian space rock: the gases trapped inside them match the Martian atmosphere as recorded by the <a href="https://mars.nasa.gov/programmissions/missions/past/viking/">Viking</a> and <a href="https://www.space.com/37722-mars-rover-curiosity-five-years-anniversary.html">Curiosity</a> missions. The meteorites can be examined in laboratories with state-of-the-art machines that are too large and heavy to fit on spacecraft. My colleagues and I have <a href="https://www.nature.com/articles/s41467-017-00513-8">just published</a> the latest such research in Nature Communications. The first detailed analysis of the eruption rates of volcanoes on Mars using Martian meteorites, it involved the Scottish Universities Environmental Research Centre, the University of Glasgow, Lawrence Livermore National Laboratory in California, and the Natural History Museum in London. </p>
<p>We examined six meteorites which had been found in various places over the last century, including the Egyptian desert (see right), Indiana in the American Midwest, and the barren ice fields of Antarctica. They had been ejected into space together around 11m years ago – this is important because it means they must have left Mars following the same asteroid impact crater on the same volcano.</p>
<p>To determine when the rocks originally erupted, we used a technique known as <a href="https://minerals.usgs.gov/science/argon-geochronology/">argon-argon geochronology</a>. This works by measuring, using a mass spectrometer, the amount of argon built up from the natural decay of potassium. It showed that the meteorites formed 1.3 billion to 1.4 billion years ago from at least four eruptions over the course of 90m years. This is a very long time for a volcano to be active, and much longer than terrestrial volcanoes, which are typically only active for a few million years. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188408/original/file-20171002-12115-99xr7y.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/188408/original/file-20171002-12115-99xr7y.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Nakhla Martian meteorite under the microscope. The colours represent volcanic minerals like olivine, pyroxene and plagioclase, also found in Earth’s volcanoes.</span>
<span class="attribution"><span class="license">Author provided</span></span>
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<p>Yet this is only scratching the surface of the volcano, since the asteroid impact will only have excavated rocks buried a few tens of metres below the surface. When we are talking about a volcano that could be upwards of 10km tall, this only represents a very small portion of its history. It must therefore have started erupting before the 1.4 billion-year-old rocks that we have been studying were formed.</p>
<p>We were also able to calculate that this volcano grew exceptionally slowly – about 1,000 times more slowly than volcanoes on Earth. This again indicates that for the Martian volcanoes to have grown so large, Mars must have been far more volcanically active in the distant past. It all serves to support the <a href="https://websites.pmc.ucsc.edu/%7Ercoe/eart290C/Additional%20Papers/Werner_MarsVolcanicHistory_Icarus09.pdf">previous findings</a> I mentioned about Martian volcanoes dating back upwards of 3.5 billion years. </p>
<h2>Knowns and unknowns</h2>
<p>The other reason for the massive size of Martian volcanoes is that Mars lacks active <a href="https://www.livescience.com/37706-what-is-plate-tectonics.html">plate tectonics</a>. This has allowed molten rock to erupt through the same parts of the planet’s crust for very long periods. For terrestrial volcanoes, by contrast, plate tectonics moves them away from their magma sources and brings their eruptions to an end.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/188625/original/file-20171003-31655-1dr2zd6.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/188625/original/file-20171003-31655-1dr2zd6.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=237&amp;fit=clip"></a>
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<span class="caption">Here Rover!</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/mars-rover-elements-this-image-furnished-468876335?src=q83yR5TWloue7k7y0yJqIA-1-44">Triff</a></span>
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<p>The last piece of the puzzle for our Martian meteorites was where they came from. By investigating NASA satellite photos we found a potential candidate: a crater large enough to have ejected meteorites into space, but young enough to be consistent with the 11 million year ejection age, and on volcanic terrain. As yet unnamed, the crater is 900km from the summit of the 12.6km Elysium Mons volcano, over 2,000km north of the present site of the NASA Curiosity rover. </p>
<p>Our research work has underlined the significant differences in volcanic activity between Earth and Mars, but numerous secrets about these Martian wonders remain. Scientists are still debating the mechanisms in the planet’s mantle that drive such volcanoes and keep supplying magma for eruptions in the same places for so long. The age of the most recent eruptions on Mars are also <a href="https://www.nasa.gov/feature/goddard/2017/mars-volcano-earths-dinosaurs-went-extinct-about-the-same-time">still subject</a> to considerable <a href="http://www.sciencedirect.com/science/article/pii/S0012821X16306057">uncertainty</a>. And there’s much still to be uncovered <a href="http://www.bbc.co.uk/news/science-environment-24624527">about the</a> links <a href="http://www.nhm.ac.uk/our-science/science-news/2015/july/opals-on-mars-could-hold-record-ancient-life.html">between</a> the planet’s volcanoes and its atmosphere. </p>
<p>Some of these secrets will continue to be unravelled through studying Martian meteorites, satellite images and new rovers. To truly understand the largest volcanoes in the Solar System, however, we will probably have to collect pieces of our neighbouring planet through human or robotic missions and bring them back to Earth.</p><img src="https://counter.theconversation.com/content/85045/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Cohen receives funding from the UK Science and Technology Facilities Council and is affiliated with the University of Glasgow and SUERC (the Scottish Universities Environmental Research Centre).</span></em></p>They erupted for billions of years and make Earth's volcanoes look like molehills. Here's what we know and what we don't know about them.Ben Cohen, Research Associate (School of Geographical and Earth Sciences), University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/838732017-09-14T19:36:56Z2017-09-14T19:36:56ZMission over: the final countdown to Cassini's fatal plunge into Saturn<figure><img src="https://images.theconversation.com/files/185933/original/file-20170914-21033-1izyggr.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">An illustration of Cassini as it plunges into Saturn’s atmosphere.</span> <span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7634/">NASA/JPL-Caltech</a></span></figcaption></figure><p>When the Cassini space probe makes its final descent into Saturn later today, data from the final nine hours of the mission will be sent back to NASA’s tracking station in Canberra, Australia.</p>
<p>As the probe descends, it will capture images and data from Saturn and its atmosphere, revealing more of the planet’s secrets. Under the spacecraft’s normal operations, its instruments first store and later forward images and data to Earth.</p>
<p>But in Cassini’s final hours, it will be transmitting home in real time, with the signals picked up by the CSIRO-managed Canberra Deep Space Communication Complex (<a href="https://www.cdscc.nasa.gov/">CDSCC</a>). </p>
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Read more:
<a href="http://theconversation.com/the-secrets-of-titan-cassini-searched-for-the-building-blocks-of-life-on-saturns-largest-moon-83441">The secrets of Titan: Cassini searched for the building blocks of life on Saturn's largest moon</a>
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<p>The CDSCC is part of NASA’s <a href="https://deepspace.jpl.nasa.gov/">Deep Space Network</a>, one of three tracking stations around the world that provide vital two-way radio contact with <a href="https://saturn.jpl.nasa.gov/the-journey/the-spacecraft/">Cassini</a> and 30 other spacecraft including <a href="https://theconversation.com/from-the-edge-of-the-solar-system-voyager-probes-are-still-talking-to-australia-after-40-years-82512">Voyagers 1 and 2</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185934/original/file-20170914-21056-jsa3wh.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185934/original/file-20170914-21056-jsa3wh.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
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<span class="caption">Cassni’s final journey in local AEST times.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7756/">NASA/JPL-Caltech/CSIRO</a></span>
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<p>Cassini’s final bonanza of data, transmitted as weak radio signals, will take 83 minutes to travel 1.5 billion km at the speed of light to reach the giant dish antennas in Canberra.</p>
<p>At an estimated 9:54pm AEST tonight (September 15), CSIRO’s team at CDSCC will capture the final signals as Cassini, travelling at more than 111,000km per hour, plunges into Saturn’s atmosphere.</p>
<p><iframe id="klVfW" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/klVfW/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>How to destroy the probe</h2>
<p>NASA decided to safely dispose of Cassini into Saturn, ending its mission as a shooting star. With the spacecraft nearly out of fuel and possible loss of control, this plan will prevent accidental collisions with any of Saturn’s moons and potential biological contamination by microbial stowaways from Earth.</p>
<p>Viewed from Saturn, the last moments of Cassini would look similar to a meteor entering Earth’s atmosphere. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185626/original/file-20170912-19546-hlhvkf.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185626/original/file-20170912-19546-hlhvkf.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">An illustration of Cassini breaking apart after entering Saturn’s atmosphere.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7635/">NASA/JPL-Caltech</a></span>
</figcaption>
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<p>From Earth, the world will await the bittersweet moment when NASA’s Jet Propulsion Laboratory mission control announces loss of signal. Cassini’s final call home will have been made.</p>
<p>It will mark the end of a <a href="https://saturn.jpl.nasa.gov/mission/about-the-mission/summary/">20-year mission</a>, a joint venture between NASA, the European Space Agency and the Italian Space Agency. </p>
<h2>Mission objectives</h2>
<p>Inspired by the earlier flypast by the twin Voyager spacecraft, the two-part mission was actually known as the <a href="https://www.jpl.nasa.gov/missions/cassini-huygens/">Cassini-Huygens mission</a>.</p>
<p>The <a href="https://saturn.jpl.nasa.gov/mission/spacecraft/cassini-orbiter/">main craft</a> was designed to study Saturn and its environs, while the piggybacking <a href="https://saturn.jpl.nasa.gov/mission/spacecraft/huygens-probe/">Huygens probe</a> was to land on Titan, the planet’s largest moon.</p>
<p>Throughout its odyssey, every step of Cassini’s journey has been followed by the dishes at CDSCC in Canberra. It was the first tracking station to make contact with Cassini after its launch from Cape Canaveral in October 1997.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185758/original/file-20170913-13626-10aat5j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185758/original/file-20170913-13626-10aat5j.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The Cassini spacecraft and Huygens probe begin their seven-year journey to Saturn after a successful launch on October 15, 1997.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/1953/">NASA</a></span>
</figcaption>
</figure>
<p>It then tracked Cassini throughout its seven-year journey to Saturn, handling the vital communications as it arrived and was placed into orbit around the planet in July 2004.</p>
<p>As the first spacecraft to orbit Saturn, it has studied <a href="https://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">the planet</a>, <a href="https://theconversation.com/the-beauty-and-mystery-of-saturns-rings-revealed-by-the-cassini-mission-83492">its rings</a> and <a href="https://theconversation.com/what-cassinis-mission-revealed-about-saturns-known-and-newly-discovered-moons-83430">its 62 moons</a>, seven of which were discovered by Cassini.</p>
<p>In 2005 the Huygens probe transmitted data as it landed safely on the surface of Titan. This was the first landing on a world in the outer Solar System.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/P7rVj_XbDnU?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The Huygens probe’s descent to Titan.</span></figcaption>
</figure>
<h2>Saturn’s wonders revealed</h2>
<p>Cassini has now witnessed almost half a Saturn year, which is 29 Earth years long.</p>
<p>While Voyagers 1 and 2 had spectacular encounters with the outer planets interspersed by years of travel, Cassini has delivered science on a daily basis. </p>
<p>Like a Swiss Army Knife of spacecraft, Cassini has a plethora of <a href="https://saturn.jpl.nasa.gov/the-journey/the-spacecraft/">scientific instruments on board</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185939/original/file-20170914-19457-vh15bk.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185939/original/file-20170914-19457-vh15bk.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Eight of Cassini’s science instruments are planned to be turned on during the final plunge, including the Ion and neutral Mass Spectrometer (INMS).</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7754/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>While the most inspiring data is the images, for staff at CDSCC the excitement has centred around performing dozens of unique radio science experiments with the Cassini team.</p>
<p>Using a process called bistatic radar, which is the deep space version of sonar, the data received made it possible to measure the size and distribution of particles in Saturn’s rings.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185786/original/file-20170913-7555-1cz8aax.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185786/original/file-20170913-7555-1cz8aax.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Saturn reigns supreme, encircled by its retinue of rings. You can also see Saturn’s famous north polar vortex and hexagon.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/6084/">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>It was also used to map the terrain and depths of ethane and methane lakes on the surface of Titan. For Cassini’s final bistatic observations of Titan earlier this year, key members of Cassini’s science team travelled to Canberra to witness the data coming into CDSCC first-hand.</p>
<p>Staff found it exhilarating to watch the pure excitement on the faces of Cassini’s team standing in their Canberra control room as the spacecraft’s faint signals were being received.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Mux5wcmqIqY?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Bistatic scattering reveals the details on Titan.</span></figcaption>
</figure>
<p>To some of us, the data may have appeared as not much more than a slightly higher peak in a hash of radio noise, but to the mission team it meant discovering a shoreline or a lake bottom on the surface of a world more than a billion kilometres away. Being a part of these discoveries was a proud moment for CDSCC and its CSIRO team.</p>
<h2>The rest of the probes</h2>
<p>As we say goodbye to Cassini, CDSCC continues to track more than 30 other spacecraft, not only NASA probes but also those of other international space agencies in Europe, Japan and India. </p>
<p>The Canberra antennas still <a href="https://theconversation.com/from-the-edge-of-the-solar-system-voyager-probes-are-still-talking-to-australia-after-40-years-82512">support both Voyager spacecraft</a> for several hours each day, receiving data from the edge of the Solar System and beyond.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185800/original/file-20170913-20593-1euwbg2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185800/original/file-20170913-20593-1euwbg2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Canberra Deep Space Communication Complex will keep track of other spacecraft after Cassini’s final plunge into Saturn.</span>
<span class="attribution"><a class="source" href="https://www.csiro.au/en/News/News-releases/2015/Australia-captures-world-first-close-ups-of-Pluto">CSIRO CDSCC</a></span>
</figcaption>
</figure>
<p>NASA’s <a href="https://www.nasa.gov/mission_pages/juno/main/index.html">Juno</a> has only just begun its primary mission, transmitting scientific data as it orbits Jupiter. Its highly elliptical orbit brings the spacecraft dangerously close to Jupiter (5,000km) before retreating away from the radiation-intense planet. </p>
<p><a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons</a>, which flew past Pluto in 2015, has set a course for an encounter with a Kuiper Belt object on January 1, 2019. The spacecraft is periodically woken from hibernation to check system functions before being returned to slumber.</p>
<p>The next few years will see a quantum shift as the Deep Space Network moves to supporting proposed human missions to the Moon, asteroids and Mars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185796/original/file-20170913-20597-1pukeup.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185796/original/file-20170913-20597-1pukeup.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Some key numbers for Cassini’s Grand Finale and final plunge into Saturn.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7657/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>For now though, CDSCC is concentrating on Cassini’s final moments, delivering its last breath of data to NASA scientists who will continue to study the information for decades to come.</p>
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<strong>
Read more:
<a href="http://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">A look back at Cassini's incredible mission to Saturn before its final plunge into the planet</a>
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<p>Using the big <a href="https://www.cdscc.nasa.gov/Pages/Antennas/dss43.html">70-metre antenna dish</a> at CDSCC as the prime receiver, it will be backed up by a smaller <a href="https://www.cdscc.nasa.gov/Pages/Antennas/dss35.html">34m dish</a>. To add even further redundancy into the system, the European Space Agency has a <a href="http://www.esa.int/Our_Activities/Operations/Estrack/New_Norcia_-_DSA_1">35m dish in New Norcia</a>, Western Australia, which will also listen to Cassini’s radio whispers.</p>
<p>Cassini’s final hours will be a bittersweet moment for the CDSCC team, losing a spacecraft that for 20 years had become a daily part of our lives.</p>
<p>We will say a fond farewell to an incredible mission, safe in the knowledge that we’ve been a part of an adventure that revealed Saturn as a real place, full of wonders, for future generations to explore.</p>
<hr>
<p><em>There are a several ways to <a href="https://saturn.jpl.nasa.gov/mission/grand-finale/for-media/#streaming">watch Cassini’s final hours</a>, including:</em></p>
<ul>
<li><em>NASA’s <a href="https://www.nasa.gov/nasalive">public channel</a></em></li>
<li><em>NASA’s Jet Propulsion Laboratory <a href="https://www.youtube.com/nasajpl/">YouTube</a> and <a href="https://www.youtube.com/nasajpl/live">YouTube Live</a> channels</em></li>
<li><em>NASA’s <a href="http://www.ustream.tv/NASAJPL2">JPL Ustream live channel</a>.</em></li>
</ul>
<p><em>You can also follow Cassini on Twitter <a href="https://twitter.com/CassiniSaturn">@CassiniSaturn</a> and Facebook at <a href="https://www.facebook.com/NASACassini">NASACassini</a>.</em></p>
<div data-react-class="Tweet" data-react-props='{"tweetId":"907801290775732225"}'></div><img src="https://counter.theconversation.com/content/83873/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Facilities Program Director NASA Operations Canberra Deep Space Communication Complex , CSIRO</span></em></p><p class="fine-print"><em><span>Richard Stephenson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The last signals from Cassini space probe before it burns up in Saturn's atmosphere will tracked by the Canberra Deep Space Communication Complex.Ed Kruzins, Facilities Program Director Nasa Operations Canberra Deep Space Communication Complex , CSIRORichard Stephenson, Deep Space Network Operations Supervisor, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834412017-09-13T05:03:41Z2017-09-13T05:03:41ZThe secrets of Titan: Cassini searched for the building blocks of life on Saturn's largest moon<figure><img src="https://images.theconversation.com/files/185043/original/file-20170907-8405-bovg44.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Cassini captures Saturn&#39;s largest moon, Titan.</span> <span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/5631/">NASA/JPL-Caltech/SSI</a></span></figcaption></figure><p>Lakes and seas of liquid methane, rain from hydrocarbon clouds, and evidence of poisonous hydrogen cyanide in the atmosphere of Titan were just some of the discoveries the Cassini probe made of Saturns’s largest moon.</p>
<p>The space probe has now made its final pass of Titan as it heads towards its grand finale plunge into the ringed planet later this week.</p>
<p>Dubbed Cassini’s “<a href="https://saturn.jpl.nasa.gov/mission/grand-finale/cassini-end-of-mission-timeline/">goodbye kiss</a>” by NASA, Titan has been the subject of much scrutiny by the probe, with <a href="https://saturn.jpl.nasa.gov/mission/grand-finale/cassini-quick-facts/">127 flybys</a> on its 13-year mission exploring the planetary system. </p>
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Read more:
<a href="http://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">A look back at Cassini's incredible mission to Saturn before its final plunge into the planet</a>
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<p>One of Cassini’s greatest feats is its contribution to untangling the complicated chemistry of Titan, no doubt one of the more chemically diverse objects in our Solar System. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185044/original/file-20170907-8366-117iuxa.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185044/original/file-20170907-8366-117iuxa.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">One last look at Titan on Cassni’s final journey.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7756/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>We have known for some time that the combination of ultraviolet rays from the Sun and particle bombardment has altered the mainly nitrogen and methane atmosphere over time.</p>
<p>This chemistry has sustained a thick, orange smog layer surrounding the entire body, shrouding Titan’s oceans and landscape from view prior to Cassini’s arrival.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185045/original/file-20170907-9189-j35vvb.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185045/original/file-20170907-9189-j35vvb.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The murky orange disk of Saturn’s moon Titan.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/3797/">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<h2>Probing Titan</h2>
<p>With Cassini’s <a href="https://saturn.jpl.nasa.gov/the-journey/the-spacecraft/">toolkit of advanced sensing instruments</a> – combined with atmospheric sampling by the <a href="https://saturn.jpl.nasa.gov/mission/spacecraft/huygens-probe/">Huygens probe</a> during its 2005 descent to the surface – the mission has developed a comprehensive picture of Titan’s chemistry.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TMxL3ZhO8A8?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Touchdown on Titan with the Huygens probe.</span></figcaption>
</figure>
<p>Intriguingly, on top of the hundreds of molecules accounted for, chemical models developed here on Earth incorporating Cassini data predict the existence of even more complex material. </p>
<p>Of potential significance to biochemistry, these molecules have evaded observation over the relatively short Cassini mission, being either out of view or present at levels below the detection limits of the equipment.</p>
<p>Even if only formed in small quantities in the atmosphere it is plausible that these life-bearing species have built up on the surface over Titan’s history.
So what are these chemicals and how do they come to be?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185593/original/file-20170912-26996-9vh08g.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185593/original/file-20170912-26996-9vh08g.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">This composite image shows an infrared view of Saturn’s moon Titan from Cassini’s flyby in November 2015. The near-infrared wavelengths in this image allow Cassini’s vision to penetrate the haze and reveal the moon’s surface.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/6278/">NASA/JPL/University of Arizona/University of Idaho</a></span>
</figcaption>
</figure>
<h2>Cyanide snow</h2>
<p>Unlike Earth, oxygen atoms are rather scarce in Titan’s atmosphere. Water is locked as surface ice and there appear to be no abundant sources of O₂ gas. </p>
<p>In oxygen’s place, we see nitrogen play a more significant role in Titan’s atmospheric chemistry.</p>
<p>Here, common products of nitrogen reactions are the cyanide family of compounds, of which hydrogen cyanide (HCN) is the simplest and most abundant.</p>
<p>As the numbers of cyanide molecules build up at lower, colder altitudes they form cloud layers of large floppy polymers (tholins) and budding ice aerosols.</p>
<p>As the aerosols descend to the surface, shells of methane and ethane ice form further layers on the exterior. This acts to protect the inner organic material on its descent to the surface before being dispersed in hydrocarbon lakes and seas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185600/original/file-20170912-28358-81yzcj.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185600/original/file-20170912-28358-81yzcj.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Cassini’s view of Titan’s high northern latitudes in May 2012, the lakes on the left are full of liquid hydrocarbons while those on the top right are only partially filled, or represent saturated ground or mudflat.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/5714/">NASA/JPL-Caltech/ASI/Cornell</a></span>
</figcaption>
</figure>
<p>Surprisingly it is these cyanide compounds, chemicals closely associated with <a href="https://emergency.cdc.gov/agent/cyanide/basics/facts.asp">toxicity and death</a> to Earthly lifeforms, that may actually provide avenues for life-bearing biomolecules to form in space environments.</p>
<p>Some <a href="http://pubs.acs.org/doi/abs/10.1021/jz501648q">simulations predict</a> that cyanides trapped in ices and exposed to space radiation can lead to the synthesis of amino acids and DNA nucleobase structures – the building blocks of life on Earth.</p>
<p>Excited by these predictions and their implications toward astrobiology, chemists have rushed to explore these reactions in the laboratory.</p>
<h2>Synchrotron experiments: Titan-in-a-can</h2>
<p>Our contributions to astrochemistry have focused on simulating the atmosphere of Titan and its cyanide haze.</p>
<p>With a specialised gas cell installed at the Australian Synchrotron, we are able to replicate the cold temperatures associated with Titan’s cloud layers. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185596/original/file-20170912-6178-t6zdtn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/185596/original/file-20170912-6178-t6zdtn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Cassini’s spectrum view of the southern polar vortex shows a signature of frozen hydrogen cyanide molecules (HCN).</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/6100/">NASA/JPL-Caltech/ASI/University of Arizona/SSI/Leiden Observatory and SRON</a></span>
</figcaption>
</figure>
<p>By injecting cyanides (the friendlier variety) into our cell we can determine the size, structure and density of Titan aerosols as they grow over time; <a href="http://pubs.rsc.org/en/content/articlelanding/2017/cp/c6cp08110j">probing with infrared light</a> from the facility. </p>
<p>These results have provided us with a list of signatures for which we can locate cyanide aerosols using infrared astronomy.</p>
<p>The next step will be to seed these aerosols with organic species to determine if they can be identified in extraterrestrial atmospheres.</p>
<p>Perhaps these signals will act as a beacon for future explorations designed to search for complex organic material in more remote space locations – potentially even on the “giant Earth” exoplanets in distant star systems.</p>
<h2>Life off Earth</h2>
<p>Space provides us a unique perspective to turn back the pages of chemistry.
Among the planets, moons and stars - and the not quite emptiness between - we can study the initial reactions thought to have started chemistry here on Earth.</p>
<p>Using ever more sensitive telescopes and advanced spacecraft, we have uncovered chemical nurseries - pockets of gas and ice exerted to harsh space radiation - in our Solar System and beyond.</p>
<p>Such cold, icy objects as Titan, the moons of Jupiter, Trans-Neptunian Objects (such as Pluto and other minor bodies in the Kuiper belt and beyond), as well as microscopic interstellar dust particles, all generate higher-order organic molecules from simple chemical ingredients.</p>
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Read more:
<a href="http://theconversation.com/cloudy-with-a-chance-of-life-how-to-find-alien-life-on-distant-exoplanets-50603">Cloudy with a chance of life: how to find alien life on distant exoplanets</a>
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<p>As far as we know, the lack of heat and liquid water precludes life to exist at these worlds. </p>
<p>However, we can look for clues regarding life’s origins on a primitive Earth. Were life-bearing chemicals delivered via comet impact, or made in-house near the early ocean shores or deep sea volcanoes? Observing the chemistry of distant objects could one day provide the answers.</p>
<p>These forays into our chemical history have been enabled by the significant steps we have taken in our exploration of space including, as a glowing example, the resounding success of Cassini’s exploration of Titan.</p><img src="https://counter.theconversation.com/content/83441/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Courtney Ennis receives funding from the Australian Research Council (DECRA Scheme). </span></em></p>The Cassini space probe discovered liquid lakes, poisonous gases and the basic elements of life on Saturn's moon, Titan.Courtney Ennis, Research Fellow, La Trobe UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834922017-09-06T04:33:02Z2017-09-06T04:33:02ZThe beauty and mystery of Saturn's rings revealed by the Cassini mission<figure><img src="https://images.theconversation.com/files/184698/original/file-20170905-13783-yq715a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Cassini makes the first radio occultation of Saturn&#39;s rings producing this simulated image with green for particles smaller than 5cm and purple where particles are larger.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA07873">NASA/JPL</a></span></figcaption></figure><p>What would Saturn be without its beautiful system of rings? Over the past 13 years, the <a href="https://www.nasa.gov/mission_pages/cassini/">Cassini space probe</a> has shown us just how <a href="https://saturn.jpl.nasa.gov/news/3089/nine-ways-cassini-matters-no-6/">complex and dynamic the rings</a> truly are. </p>
<p>The 20-year mission is coming to an end later this month when the probe makes its final <a href="https://saturn.jpl.nasa.gov/mission/grand-finale/cassini-end-of-mission-timeline/">destructive plunge</a> into Saturn.</p>
<p>As part of its grand finale, Cassini has flown closer to the rings than ever before, first <a href="https://saturn.jpl.nasa.gov/news/2966/ring-grazing-orbits/">grazing the outermost edges of the rings</a> before taking the risky leap of <a href="https://saturn.jpl.nasa.gov/news/3032/nasa-spacecraft-dives-between-saturn-and-its-rings/">diving through the gap</a> between the rings and Saturn. </p>
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Read more:
<a href="http://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">A look back at Cassini's incredible mission to Saturn before its final plunge into the planet</a>
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<h2>Saturn’s big empty</h2>
<p>One of the surprises was that it’s <a href="https://saturn.jpl.nasa.gov/news/3034/cassini-finds-the-big-empty-close-to-saturn/">quite empty in this gap</a>. This is very different to when Cassini was bombarded by hundreds of dust particles per second as it moved past the outer rings late last year.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MXmAuaomZQQ?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The sound of outer ring particles hitting the Cassini spacecraft.</span></figcaption>
</figure>
<p>But it meant good news for the mission as this final stage had a better chance for success if there was less material in the way. </p>
<p>During a <a href="https://www.nasa.gov/image-feature/jpl/pia21886/cassinis-inside-out-rings-movie">recent ring dive in August</a>, instead of orientating Cassini so that it flew antenna-first through the gap (offering it more protection), the spacecraft was turned around allowing it to capture a fantastic view of the rings as it dived past. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fprD6Nssu24?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Cassini’s four-minute dive through the ring gap on August 20, 2017.</span></figcaption>
</figure>
<h2>Know your ring ABCs</h2>
<p>Over the centuries, as Saturn’s rings have been observed in finer detail, they have been broken into discrete sections. They are named alphabetically in order of discovery, which means from innermost to outermost the order is D, C, B, A, F, G and E.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rM1HAfLAEw8?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The ring labels by discovery.</span></figcaption>
</figure>
<p>Saturn’s innermost ring D is much less dense and therefore fainter than its neighbouring ring C.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184668/original/file-20170905-28059-90i3v3.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184668/original/file-20170905-28059-90i3v3.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Observing the rings close to Saturn - the D ring is faint while in the lower part of the image the C ring is overexposed.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/6185/">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>By comparing new Cassini images of the D ring with its original discovery image from Voyager in 1980, it’s possible to see changes in the ring over a relatively short period of time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184669/original/file-20170905-28036-ebcbq5.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184669/original/file-20170905-28036-ebcbq5.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Comparing images of the D ring taken 25 years apart. The inset shows the fine detail achieved by Cassini.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA07714">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>In the Voyager image, three relatively bright arcs can be seen in the D ring (the bright arc in the lower left of frame is the C ring). Most dramatically, the central and brightest arc has faded markedly and moved 200km closer to Saturn (the arc no longer lines up with the Voyager image). </p>
<h2>Origin of the rings</h2>
<p>We know that the rings are <a href="https://saturn.jpl.nasa.gov/science/rings/">mostly made of water ice</a>, but it’s not clear how they formed or even how old they are. </p>
<p>The fact that they are still bright, rather than coated in dust, suggests a young age – perhaps <a href="https://theconversation.com/saturns-moons-may-be-younger-than-the-dinosaurs-so-could-life-really-exist-there-56860">just 100 million years old</a>, placing their formation in the time of the dinosaurs. </p>
<p>This is <a href="http://www.seti.org/seti-institute/press-release/moons-saturn-may-be-younger-dinosaurs">consistent with Cassini data</a>, but this theory also presents a problem: it means that a previous collection of moons had a fairly recent and mighty smash-up, creating the rings and five of Saturn’s current-day moons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184703/original/file-20170905-13709-1nlekyx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184703/original/file-20170905-13709-1nlekyx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">A true colour image of Saturn’s rings. The bright dot above and to the right of centre is the planet Venus.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA14935">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>Alternatively, Cassini has also shown that there is a <a href="https://www.nature.com/news/dust-reveals-ancient-origin-for-saturn-s-rings-1.15743">lot less dust entering the Saturn system</a> than was originally expected. This makes it possible for the rings to be both ancient and bright, having formed early in the life of the Solar System. Furthermore, interactions within the rings might dust them off and keep them looking young. </p>
<h2>Finger on the source</h2>
<p>For Saturn’s <a href="https://planetarynames.wr.usgs.gov/Page/Rings#saturn">outermost E ring</a> the source is pretty clear. The moon <a href="https://saturn.jpl.nasa.gov/science/enceladus/">Enceladus</a> orbits within this ring and Cassini observations have <a href="https://saturn.jpl.nasa.gov/news/2532/icy-tendrils-reaching-into-saturn-ring-traced-to-their-source/">directly traced features</a> in the ring back to <a href="https://saturn.jpl.nasa.gov/resources/4852/">geysers erupting</a> from Enceladus’s surface.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184676/original/file-20170905-28030-hwz1u2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184676/original/file-20170905-28030-hwz1u2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Direct observations are well-matched with computer simulations that model the trajectories of tiny icy grains ejected from Enceladus’s geysers.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA17191">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>While in the <a href="https://planetarynames.wr.usgs.gov/Page/Rings#saturn">faint F ring</a>, the moon <a href="https://saturn.jpl.nasa.gov/resources/6280/">Prometheus</a> creates streamer-channels, drawing material out of the ring. </p>
<p>Prometheus interacts with the ring once every orbit, when it reaches the point that takes it furthest away from Saturn and closest to the F ring. As Prometheus orbits faster than the ring material, a new streamer is created that is ahead of the old one with every orbit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184678/original/file-20170905-28095-1u2d7w0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184678/original/file-20170905-28095-1u2d7w0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">A series of streamer-channels drawn out by the moon Prometheus.</span>
<span class="attribution"><span class="source">NASA/JPL/Space Science Institute</span></span>
</figcaption>
</figure>
<h2>Bulging waistlines</h2>
<p>Several of Saturn’s smaller moons reside within and carve out gaps in the rings, and Cassini has shown them to have bulges around their middles.</p>
<p>The moon <a href="https://saturn.jpl.nasa.gov/resources/7616/">Pan</a> was responsible for clearing the A ring’s large <a href="https://www.nasa.gov/jpl/cassini/pia17161/#.Wa04rVUjHio">Encke Gap</a>. As it collects the ring material, Pan’s gravity is not strong enough to spread the accumulated matter across its surface, and instead a striking ridge develops. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184129/original/file-20170831-29609-fzetpx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184129/original/file-20170831-29609-fzetpx.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Gorging on material from Saturn’s rings these moons have grown round around the middle.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/pia21449/small-wonders">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>The tiny moon Daphnis is <a href="https://solarsystem.nasa.gov/planets/daphnis">one of seven moons newly discovered</a> by Cassini. It is just 8km across and as it orbits inside the A ring’s small <a href="https://en.wikipedia.org/wiki/Rings_of_Saturn#Keeler_Gap">Keeler Gap</a>, it pulls on the ring particles leaving waves in its wake. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184836/original/file-20170906-9851-158ju0a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184836/original/file-20170906-9851-158ju0a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Daphnis raises waves in Saturn’s rings as it passes by.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA17212">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<h2>Turning rings into moons</h2>
<p>Cassini has spotted signs of a <a href="https://www.jpl.nasa.gov/news/news.php?release=2014-112">potential new moonlet forming</a> on the very edge of <a href="https://planetarynames.wr.usgs.gov/Page/Rings#saturn">Saturn’s bright A ring</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184304/original/file-20170901-21670-1nbo3g8.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184304/original/file-20170901-21670-1nbo3g8.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Caught in action: Saturn’s rings giving birth to a new tiny moon, see the disturbance visible at the outer edge of the planet’s A ring.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/6008/?category=images">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>The newly formed object is probably less than a kilometre across but being able to see such a process in action was a complete surprise for Cassini scientists.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/what-cassinis-mission-revealed-about-saturns-known-and-newly-discovered-moons-83430">What Cassini's mission revealed about Saturn's known and newly discovered moons</a>
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<p>It supports the theory that long ago, Saturn’s rings could have been much more massive and capable of <a href="https://phys.org/news/2010-06-formation-saturn-moons.html">producing some of the moons</a> that exist today.</p>
<p>It also potentially provides insight into how the planets of the solar system formed, emerging out of the accretion disk that once orbited the young Sun.</p>
<p>Cassini has certainly achieved its mission objectives to explore Saturn, its atmosphere, magnetosphere and rings and to study Saturn’s moons, particularly Titan. So much has been learned, including the ability to gaze with wonder and awe at the amazing Solar System we are part of.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184705/original/file-20170905-13709-1ab6m6a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184705/original/file-20170905-13709-1ab6m6a.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Looking back: The pale blue dot of the Earth can be seen below Saturn’s rings in this image Cassini captured on July 19, 2013.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Space Science Institute</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/83492/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Cassini space probe took us up close and through the beautiful rings of Saturn. It captured some amazing images, and even the sound of the rings during its mission.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834302017-09-05T06:18:45Z2017-09-05T06:18:45ZWhat Cassini's mission revealed about Saturn's known and newly discovered moons<figure><img src="https://images.theconversation.com/files/184629/original/file-20170905-20461-1l0kw8p.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">A Cassini portrait of five of Saturn&#39;s moons. Janus (179km across) is on the far left, Pandora (81km across) orbits between the A ring and the thin F ring, Enceladus (504km across) is centre, Rhea (1,528km), is bisected by the right edge of the image and the smaller moon Mimas (396km) is seen beyond Rhea also on the right side of the image.</span> <span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA14573">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p>The <a href="https://www.nasa.gov/mission_pages/cassini/">Cassini space probe</a> not only visited Saturn as part of its mission, it also revealed many of the planet’s moons in stunning detail and showed them to be <a href="https://saturn.jpl.nasa.gov/news/3088/nine-ways-cassini-matters-no-5/">interesting and unique worlds</a>. </p>
<p>The 20-year mission is coming to an end later this month when the the probe makes its final <a href="https://saturn.jpl.nasa.gov/mission/grand-finale/cassini-end-of-mission-timeline/">destructive plunge</a> into Saturn.</p>
<p>Thirteen of those years were spent orbiting the ringed planet, the second largest in our Solar System, exploring some of Saturn’s 62 moons, seven of which were discovered by Cassini. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184636/original/file-20170905-28059-1e4ygrv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184636/original/file-20170905-28059-1e4ygrv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Cassini’s moon mission overview: This graphic summarises Cassini’s 13 years orbiting Saturn, with moon flybys grouped into rows.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7757/">NASA/Jet Propulsion Laboratory-Caltech</a></span>
</figcaption>
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<hr>
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<strong>
Read more:
<a href="http://theconversation.com/a-look-back-at-cassinis-incredible-mission-to-saturn-before-its-final-plunge-into-the-planet-83226">A look back at Cassini's incredible mission to Saturn before its final plunge into the planet</a>
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<h2>A Titan of a moon</h2>
<p><a href="https://solarsystem.nasa.gov/planets/titan">Titan</a>, the largest of Saturn’s moons, is the only moon in the Solar System with a substantial atmosphere. In fact, Titan’s atmosphere is so dense that walking on its surface would be like swimming at the bottom of a pool here on Earth. </p>
<p>In 2009, Cassini confirmed that <a href="https://saturn.jpl.nasa.gov/news/1195/resolving-rain-over-xanadu/">Titan has lakes, clouds and rain</a> – a “water” cycle of sorts, but driven by liquid methane. It’s so cold on Titan that water forms ice as hard as granite and is the stuff of mountains rather than rivers. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/RrGPtCdItBw?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">A closer look at Titan’s lakes and landscapes.</span></figcaption>
</figure>
<p>Titan’s lakes are mostly found in the northern hemisphere, while <a href="https://saturn.jpl.nasa.gov/resources/5702/">mountains loom over Titan’s equator</a>, suggesting tectonic and cryovolcanic activity at work. The two dark strips in the image below are dune-filled regions (or <a href="http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2804.pdf">sand seas</a>) called Fensal (northward) and Aztlan (southward).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184112/original/file-20170831-24226-rvmn5u.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184112/original/file-20170831-24226-rvmn5u.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Cassini used radar and near-infrared imaging to peer below Titan’s thick atmosphere and map the surface details.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/5-peering-through-titans-haze">NASA/JPL/University of Arizona/University of Idaho</a></span>
</figcaption>
</figure>
<h2>Tiny Enceladus packs the biggest surprise</h2>
<p>The <a href="https://saturn.jpl.nasa.gov/news/2916/cassini-at-enceladus-a-decade-plus-of-discovery/">big surprise for the Cassini mission</a> was discovering that the small moon <a href="https://solarsystem.nasa.gov/planets/enceladus">Enceladus</a>, just 500km across, has all the right stuff for life – water, energy and nutrients, powered by <a href="https://theconversation.com/water-water-everywhere-in-our-solar-system-but-what-does-that-mean-for-life-76315">hydrothermal vents</a> deep on the ocean floor. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184115/original/file-20170831-24237-1fni2m.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184115/original/file-20170831-24237-1fni2m.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Salty water gushes out of more than 100 geysers on Enceladus and feeds Saturn’s diffuse outer E ring.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/4852/">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<h2>Case closed: the mystery of the disappearing moon</h2>
<p>In 1671 the Italian astronomer <a href="https://www.britannica.com/biography/Gian-Domenico-Cassini">Giovanni Cassini</a> discovered Saturn’s third-largest moon, <a href="https://solarsystem.nasa.gov/planets/iapetus">Iapetus</a>, only to have it briefly disappear before becoming visible again a year later. He surmised that Iapetus might have two contrasting sides - one bright and easy to see, the other so dark to render it invisible. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184320/original/file-20170901-26069-h693og.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184320/original/file-20170901-26069-h693og.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Iapetus has a dark dusty side and a bright icy side.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA11690">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>More than three centuries later, the Cassini spacecraft revealed the reason why. The dark side of Iapetus is <a href="http://news.cornell.edu/stories/2009/12/cassini-unveils-history-saturns-moon-iapetus">coated in dust</a> from Saturn’s outer moon Phoebe. Iapetus and <a href="https://solarsystem.nasa.gov/planets/phoebe">Phoebe</a> orbit in opposite directions with Iapetus ploughing into debris ejected from Phoebe’s surface. </p>
<p>This debris forms an <a href="https://science.nasa.gov/science-news/science-at-nasa/2009/07oct_giantring">incredibly dark but giant outer ring</a> around Saturn that follows Phoebe’s orbit and is tilted relative to the planet’s main rings.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184619/original/file-20170905-14281-m05lcf.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184619/original/file-20170905-14281-m05lcf.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">NASA’s Spitzer Space Telescope used its infrared camera to discover Phoebe’s dark but giant ring.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA12256">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>Cassini showed that the dust covering Iapetus slightly raises the temperature on that side so that ice cannot settle there. This means dark spots become darker, while water vapour transfers to the moon’s other side making it even brighter. That’s how Iapetus maintains its dichotomy. </p>
<p>What’s more, as seen in the Cassini flyover below, Iapetus also has a mountainous ridge that runs more than three-quarters of the way around the moon’s equator. Due to its location and the very steep slope of its peaks it has been suggested that Iapetus may have once <a href="http://www.planetary.org/blogs/emily-lakdawalla/2012/3389.html">had its own ring of debris</a> which has since collapsed down onto the moon, creating the ridge in the process.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/DYvITG_TDfE?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Flying over the ridge on Iapetus.</span></figcaption>
</figure>
<h2>Oh the places we’ve seen</h2>
<p>Saturn has seven major moons with diameters of 400km or more. Besides Titan, Enceladus and Iapetus the list also includes <a href="https://solarsystem.nasa.gov/planets/mimas">Mimas</a>, <a href="https://solarsystem.nasa.gov/planets/tethys">Tethys</a>, <a href="https://solarsystem.nasa.gov/planets/dione">Dione</a> and <a href="https://solarsystem.nasa.gov/planets/rhea">Rhea</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184624/original/file-20170905-9740-hjqxmv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184624/original/file-20170905-9740-hjqxmv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Mimas, the real-life moon that mimics science fiction.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7581/">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>Any science fiction fan will recognise in Mimas a resemblance to the famed <a href="http://www.starwars.com/databank/death-star">Death Star</a> from the Star Wars movies. </p>
<p>The feature responsible for this resemblance is the Herschel crater, nearly 140km wide or about a third of the diameter of Mimas. If the impact had been any bigger it might have destroyed Mimas completely. Rising from the centre of the crater is a mountain that’s almost as tall as Mount Everest.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184625/original/file-20170905-9729-tq6q3l.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184625/original/file-20170905-9729-tq6q3l.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The two faces of Tethys: cratered on the left and canyon on the right.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/7590/">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>Tethys also shows the scars of a major impact and to put it into perspective, the Odysseus Crater on Tethys (seen on the left image above) is as wide as Mimas. On Tethys’ opposite side is the Ithaca Chasma, a deep canyon that runs the majority of the way around the icy moon.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">Bittersweet feeling as Cassini mission embarks on its 'grand finale' ahead of death plunge</a>
</strong>
</em>
</p>
<hr>
<p>The Cassini spacecraft flew close enough to the icy moons <a href="https://www.nasa.gov/mission_pages/cassini/whycassini/cassini20101126.html">Rhea</a> and <a href="https://www.nasa.gov/mission_pages/cassini/whycassini/cassini20120302.html">Dione</a> that it could sniff their tenuous atmospheres and discovered evidence of oxygen.</p>
<p>The oxygen is at levels <a href="https://www.nasa.gov/mission_pages/cassini/whycassini/cassini20120302.html">5 trillion times less dense</a> than Earth. It appears to be released by sunlight or energetic particles hitting the moon and breaking down the water ice on the surface.</p>
<p><a href="https://solarsystem.nasa.gov/planets/hyperion">Hyperion</a> may not be one of Saturn’s major moons, but it certainly has an appearance that’s out of this world. The moon is highly porous and has a very low density. It’s thought that any impacts simply compress the moon, just like sticking your thumb into a sponge to mould the surface. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184122/original/file-20170831-24286-9ys7f9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184122/original/file-20170831-24286-9ys7f9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Hyperion, the largest of Saturn’s irregular (or non-round) moons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/jpl/cassini-sends-final-close-views-of-odd-moon-hyperion">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<hr>
<p><em>Next I’ll explore what <a href="https://theconversation.com/the-beauty-and-mystery-of-saturns-rings-revealed-by-the-cassini-mission-83492">Cassini has shown us of Saturn’s rings</a> and the moons that reside there.</em></p>
<hr><img src="https://counter.theconversation.com/content/83430/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museum Victoria</span></em></p>The Cassini space probe discovered several new moons on its mission to Saturn, and revealed fresh views of the moons we already knew about.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/832262017-09-04T06:36:08Z2017-09-04T06:36:08ZA look back at Cassini's incredible mission to Saturn before its final plunge into the planet<figure><img src="https://images.theconversation.com/files/184465/original/file-20170904-8510-1ravrm8.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">An illustration of Cassini diving between Saturn and the planet&#39;s innermost ring.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>The <a href="https://www.nasa.gov/mission_pages/cassini/">Cassini space probe</a> mission is coming to an end this month when the probe makes its final <a href="https://saturn.jpl.nasa.gov/mission/grand-finale/cassini-end-of-mission-timeline/">destructive plunge</a> in to Saturn. It’s spent the past thirteen years studying the planet, its rings and moons in unprecedented detail.</p>
<p>Cassini wasn’t the first NASA probe to study Saturn close-up. <a href="https://solarsystem.nasa.gov/missions/pioneer11">Pioneer 11</a> (1979), <a href="https://solarsystem.nasa.gov/missions/voyager1">Voyager 1</a> (1980) and <a href="https://solarsystem.nasa.gov/missions/voyager2">Voyager 2</a> (1981) had flown by Saturn earlier, not stopping but giving us the opportunity to see the planet as the amazing world that it is. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184093/original/file-20170831-24267-5wsy1v.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184093/original/file-20170831-24267-5wsy1v.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Pioneer 11 was the first spacecraft to fly by Saturn, September 1, 1979.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_2483.html">NASA Ames</a></span>
</figcaption>
</figure>
<p>But to really understand a planet, you need to spend time with it and that’s what Cassini has done.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/from-the-edge-of-the-solar-system-voyager-probes-are-still-talking-to-australia-after-40-years-82512">From the edge of the Solar System, Voyager probes are still talking to Australia after 40 years</a>
</strong>
</em>
</p>
<hr>
<p>Launched in 1997, it took almost seven years to reach Saturn, entering orbit on July 1, 2004. On Christmas Day that year, the <a href="https://saturn.jpl.nasa.gov/mission/spacecraft/huygens-probe/">Huygens probe</a> was released towards Titan, the first probe ever to land on an object in the outer Solar System.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/KreECFCGEI0?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The Huygens probe.</span></figcaption>
</figure>
<p>Cassini was on a four year mission to explore Saturn, its atmosphere, magnetosphere, rings and to study Saturn’s moons, especially Titan the only moon in the Solar System to have a substantial atmosphere. </p>
<h2>Time goes by and seasons change</h2>
<p>But four years has quickly grown into 13 impressive years, allowing Cassini to watch the slow progression of Saturn’s changing seasons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184097/original/file-20170831-24251-kenp06.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184097/original/file-20170831-24251-kenp06.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The colours of Saturn’s seasons: clear winter blue in the north, smoggy summer yellow in the south.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA05380">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>When the spacecraft arrived, Saturn’s northern hemisphere was in the dark of winter. </p>
<p>The northern part of Saturn was a mesmerising blue. Less sunlight, particularly the Sun’s harsh ultraviolet rays, could reach the north leaving the atmosphere clear of smog and giving rise to the beautiful blue scattered light. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184308/original/file-20170901-4580-1cbuqy9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184308/original/file-20170901-4580-1cbuqy9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The icy moon Mimas passes in front of the clear blue sky of winter at Saturn.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_264.html">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>In August 2009, Cassini had the opportunity to view <a href="https://saturn.jpl.nasa.gov/resources/695/">Saturn at equinox</a>, a special time when the Sun sits directly in line with the planet’s rings. The only light hitting the rings is reflected light from Saturn itself. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184099/original/file-20170831-25683-1d65xv9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184099/original/file-20170831-25683-1d65xv9.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The first time we’ve seen a close up view of Saturn at equinox. The rings have been artificially brightened to bring them into view.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/centers/goddard/news/topstory/2009/rings_equinox.html">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>During this time shadows were seen dancing across the rings. On average, the rings are very thin, just ten metres or so in thickness, and each of the rings and gaps in the rings have a <a href="https://planetarynames.wr.usgs.gov/Page/Rings">special name</a>. </p>
<p>At the edge of Saturn’s B ring, the equinox shadows revealed structures that towered as high as 2.5 kilometres. Quite possibly, small moonlets are splashing the ring particles about and forcing them upwards as the moonlets pass by. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184104/original/file-20170831-24267-hhtqs2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184104/original/file-20170831-24267-hhtqs2.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Towering structures cast shadows on Saturn’s B ring.</span>
<span class="attribution"><a class="source" href="https://saturn.jpl.nasa.gov/resources/5115/">NASA/JPL/Space Science Institute</a></span>
</figcaption>
</figure>
<p>As Cassini’s mission comes to an end, summer has arrived at Saturn’s north. The colours are changing and right at the top of Saturn’s north pole, it’s possible to see the distinctive hexagon – a six-sided weather pattern that is now bathed in sunlight. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184105/original/file-20170831-24286-1uguwdn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/184105/original/file-20170831-24286-1uguwdn.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Cassini has spent half a Saturn year in orbit watching the slow progression of the seasons.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech/Space Science Institute</span></span>
</figcaption>
</figure>
<p>Embedded in the heart of the hexagon is a roaring hurricane, 50 times larger than any hurricane experienced on Earth. Simulations suggest that it is <a href="https://www.space.com/30608-mysterious-saturn-hexagon-explained.html">produced by a jet stream</a> curving around Saturn’s north pole and being jostled about as it interacts with other air currents. </p>
<p>Whatever established the hexagon, it’s certainly long-lived. The pattern was <a href="https://www.nasa.gov/mission_pages/voyager/hexagon_PIA_11682.html">first recorded by the Voyager spacecraft</a> in 1980, although it was not discovered in the data until eight years later.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/BBQ_rnkqtpk?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Several different views of Saturn’s unique hexagon.</span></figcaption>
</figure>
<h2>Pink dancing lights</h2>
<p>The Hubble Space Telescope has captured strong aurora on Saturn <a href="http://hubblesite.org/image/1654/news_release/2005-06">at ultraviolet wavelengths</a>. But for the first time, Cassini has shown us Saturn’s <a href="https://saturn.jpl.nasa.gov/resources/698/">northern</a> and southern lights shimmering above the planet in visible light. </p>
<p>Unlike Earth’s aurora which are predominantly green and blue due to the oxygen and nitrogen in our atmosphere, Saturn’s aurora <a href="https://arxiv.org/abs/1506.00664">vary from pink to purple</a> as charged particles collide and excite the hydrogen-rich atmosphere.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/vonWHtWdYUY?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The auroras over Saturn.</span></figcaption>
</figure>
<h2>Scientists pay tribute to Cassini</h2>
<p>The Cassini mission has been a fantastic international achievement made possible via <a href="https://www.nasa.gov/mission_pages/cassini/main/index.html">NASA</a> and the European Space Agency (<a href="http://sci.esa.int/cassini-huygens/">ESA</a>).</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/planet-or-dwarf-planet-all-worlds-are-worth-investigating-74682">Planet or dwarf planet: all worlds are worth investigating</a>
</strong>
</em>
</p>
<hr>
<p>It has involved 17 countries, 260 scientists plus thousands more who worked to design, build and launch the spacecraft.</p>
<p>Team members who have spent their careers working on the Cassini mission reflect on the epic journey. So farewell Cassini, what an amazing time it’s been. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fHaaIX-iSqM?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">Remembering Casssini.</span></figcaption>
</figure>
<hr>
<p><em>Next I’ll take a closer look at <a href="https://theconversation.com/what-cassinis-mission-revealed-about-saturns-known-and-newly-discovered-moons-83430">Cassini’s observations of many of the known moon’s of Saturn</a> as well as the space probe’s new discoveries.</em></p>
<hr><img src="https://counter.theconversation.com/content/83226/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>With only days to go before NASA's Cassini space probe ends its two-decade mission to explore Saturn, what has it revealed about the ringed planet, the second largest in our solar system?Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/828502017-08-28T11:49:27Z2017-08-28T11:49:27ZThe PLATO mission: an investigation of planetary systems<figure><img src="https://images.theconversation.com/files/182947/original/file-20170822-30491-6n6gqk.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Two spacecraft concepts for the Plato mission.</span> <span class="attribution"><a class="source" href="http://sci.esa.int/plato/46683-spacecraft-concepts-for-the-plato-mission/">ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Despite its proximity to the Earth, the Sun still poses many questions. But what do we know of other stars, located at immense distances on a human scale? How are they different from the Sun? Are they also hosting planets such as those that revolve around our Sun?</p>
<p>To answer these questions, we will soon have a powerful new tool: the <a href="http://sci.esa.int/plato/">PLATO mission</a> (for “PLAnetary Transits and Oscillations of stars”), led by the European Space Agency (ESA) with a consortium of laboratories and national space agencies. </p>
<h2>The transit method</h2>
<p>What are PLATO’s objectives? Like other missions to detect <a href="https://en.wikipedia.org/wiki/Exoplanet">exoplanets</a>, PLATO uses the transit method: when a planet passes (“transits”) between its star and the observer, it hides a small part of the stellar disc and this lowers the brightness of the star (by about 0.01%). This method has been used by other space missions such as Corot and Kepler. Thus, thousands of exoplanets have been detected in orbit around other stars in our galaxy.</p>
<p>PLATO goes further than this simple detection. The Sun and the stars generally are the seat of vibrations that occur on the surface as large waves raising and lowering alternatively the surface of the star. These movements come with compressions and expansions of the plasma that makes up the star, which in turn induce changes in brightness. PLATO can detect these changes. The surface movements are just the visible part of (mostly acoustic) waves which propagate throughout the whole star, down to its centre for some of these waves. They are therefore detected on the surface but carry information about the inner layers of the star: temperature, density, etc. We can thus draw a measure of the average density of the star as well as information on the structure of the centre, where the nuclear fusion reactions providing energy to the star take place.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179251/original/file-20170721-28505-1s6op4n.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">PLATO in space. Artist’s view.</span>
<span class="attribution"><span class="source">ESA</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>These observations are used to characterise the star in terms of mass, size (star radius) and age, in a very precise manner thanks to this seismic analysis, by far the most powerful analysis for these measures. This is a fundamental aspect: many planets have already been detected, many stars have already been surveyed seismically, but very few stars have been the object of these two simultaneous analyses. This is the major asset of the PLATO mission: it will realise this double analysis for tens of thousands of stars.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/179252/original/file-20170721-28488-xmd099.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=237&amp;fit=clip">
<figcaption>
<span class="caption">Telescopes in Hawaii.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
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<p>Another one of PLATO’s assets is its complementarity with observations using ground-based telescopes. Indeed, observations from the ground can enrich the results obtained from space observations. PLATO focuses on relatively bright stars, which greatly facilitates the task of the ground-based telescopes. The characterisation of the stars and planets that surround them will thus be easier.</p>
<h2>Long periods of observation</h2>
<p>PLATO can pursue several scientific goals. First, it can detect a large number of planetary systems around stars other than ours. Special attention will be paid to systems similar to ours. Here comes another advantage: its analyses rely on very long periods of observations (typically two years). Thus, we can detect a large number of planets that have an orbit with a similar period to that of Earth or other planets in our system (a Martian “year” lasts 687 days). Thus, we may be able to identify a planet similar to Earth around a star similar to the Sun.</p>
<p>Research will focus more generally on planets that are at a given distance from their host star, so that the expected temperature is compatible with the existence of water in liquid form. This criterion, which is certainly too simple to embrace the complexities of planetary atmospheres, gives an idea of the “habitability” of a planet, that is to say the possibility for a life form similar to that found on Earth to thrive.</p>
<h2>Hot Jupiters</h2>
<p>Beyond this, PLATO will also focus on so-called exotic systems. Planetary systems observed so far are very often quite different from ours. In particular, some have what are now called hot Jupiters: planets the size of Jupiter but with an orbit very close to their host star, while “our” Jupiter is far from the Sun and presents a very low surface temperatures (less than -100 °C). The discovery of these very different systems, compared to ours, was a great surprise. Indeed, it was thought that the process of planet formation around a star led to rocky planets of small size near the star (such as Mercury, Venus, Earth and Mars) and giant gaseous planets further away from the star (such as Jupiter, Saturn, Uranus, and Neptune).</p>
<p>In this quest, we must however take into account what is called an “observational bias”: on the one hand, the large planets like Jupiter are easier to detect than small planets like Earth. So, we will detect them in larger numbers. On the other hand, the laws of physics tell us that a planet close to its star will have a short period. Less observation time is then needed to detect them, which creates another favourable bias. Indeed, some of these hot Jupiters are so close to their star that they make a complete circuit around it in just four or five days. To discover them, no need to observe the 10 years that the revolution of our Jupiter around our Sun lasts.</p>
<h2>Exotic systems</h2>
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<img alt="" src="https://images.theconversation.com/files/179253/original/file-20170721-28505-widoc1.JPG?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=237&amp;fit=clip">
<figcaption>
<span class="caption">Image of a hypothetical planet ocean with a terrestrial atmosphere and two satellites..</span>
<span class="attribution"><span class="source">Lucianomendez/Wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>However, these “exotic” systems do indeed exist. The question that therefore arises is to understand why they are so different from ours. To do so, we need to understand the system in its entirety, star <em>and</em> planets. So we need to know their characteristics. What is the size and mass of the star? The seismic analysis will tell us that. It will then assess the mass and size of the planets, which are measured in relative terms compared to those of the host star. It is the same for the age of the system: the planets and central star form at about the same time, so measuring the star age by a seismic analysis allows us to know the age of the planets that surround it. And so to know if the system just formed or if it has been evolving for billions of years. All this will provide a comprehensive view on which scientists can try to figure out how the planetary systems form and evolve.</p>
<p>It is this task that the scientists of all nationalities involved in the PLATO mission will tackle. But there is still a long way to go, since the launch is planned for 2027.</p><img src="https://counter.theconversation.com/content/82850/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frédéric Baudin has received financing from the CNES and the ANR.</span></em></p><p class="fine-print"><em><span>Sophie Félix does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>While we on Earth are familiar with our own star, the Sun, the European Space Agency's PLATO mission will explore solar systems similar to ours as well as those that are more exotic.Frédéric Baudin, Enseignant-Chercheur à l'Institut d'Astrophysique Spatiale, Université Paris Sud – Université Paris-SaclayLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/827982017-08-23T08:22:33Z2017-08-23T08:22:33ZHere's the blueprint for a global fireball observatory – and why we need one<figure><img src="https://images.theconversation.com/files/182802/original/file-20170821-4987-91zqm6.png?ixlib=rb-1.1.0&amp;rect=0%2C2%2C786%2C519&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption"></span> </figcaption></figure><p>Bright shooting stars are one of nature’s great wonders. Like the one in the main image, which was <a href="http://www.devonlive.com/watch-as-a-fireball-lights-up-the-skies-over-south-devon/story-30369572-detail/story.html">visible from</a> Devon in the south-west of England in June, these fireballs are caused by space rocks hitting Earth’s atmosphere. The friction forces them to slow down, producing a tremendous amount of heat at the same time. If the rock is big enough, a fragment will survive this fiery transition and fall to Earth as a meteorite. </p>
<p>Planetary scientists study these rocks to extract clues as to how our solar system formed. But this work is complicated by the fact that we don’t know where in the solar system most of Earth’s <a href="https://www.lpi.usra.edu/meteor/">50,000 or so meteorites</a> came from. </p>
<p>To improve this situation, you have to determine a new fireball’s orbit once it breaches Earth’s atmosphere. This means observing it from multiple angles. You then ideally want to recover the meteorite before the weather changes the chemistry of the sample – usually in the first shower of rain. A new network of cameras is being set up in the UK to help in this endeavour, phase two of a global network that started five years ago in Australia. </p>
<h2>Fireball hunting</h2>
<p>Meteorites are arriving from outer space all the time. About 50 tonnes of extraterrestrial material enters Earth’s atmosphere each year. Most are sand-sized particles known as cosmic dust, including the majority of the <a href="https://www.space.com/37829-perseid-meteor-shower-2017-skywatcher-photos.html">Perseid meteor shower</a> that took place earlier in August. </p>
<p>But even over a relatively small space like the UK, <a href="http://www.lpi.usra.edu/books/MESSII/9021.pdf">about 20 meteorites</a> of a searchable size land each year – of which the Devon fireball was a good example. Most are barely 10g, about the size of a six-sided dice. Two or three will be bigger; usually up to a kilogram in mass or the size of a tennis ball. </p>
<p>This is but a remnant of the 6,000 to 20,000 meteorites in the same size range that we see each year in the land mass of the world as a whole. Yet observing and finding these is still no mean feat. To date, only around 30 meteorites <a href="http://www.meteoriteorbits.info/">have been recovered</a> after their fireball was observed. This has mostly been through remote camera networks including in Canada, France, the Czech Republic, Finland and Australia. </p>
<p>Such networks are continuously imaging the night sky over a huge area, which is ideal for tracking orbits back to space and reaching the landing site fast. I used to work as a researcher for the <a href="https://theconversation.com/how-to-find-a-meteorite-thats-fallen-to-earth-52906">Desert Fireball Network</a> in Australia. Since it was set up five years ago, its 52 cameras have found four meteorites. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182826/original/file-20170821-4969-9p19yd.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182826/original/file-20170821-4969-9p19yd.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">One of the cameras in the Nullarbor Desert in southern Australia.</span>
<span class="attribution"><span class="source">DFN</span></span>
</figcaption>
</figure>
<p>The project to extend the Desert Fireball Network has already seen three high-resolution cameras installed in different parts of England in recent months, along with sophisticated image-processing software. A further seven will be in place by next summer, in a collaboration between Imperial College London, University of Glasgow, the Open University, the Natural History Museum and Curtin University in Perth, Australia. </p>
<p>The new network will track any fast-moving object flying across the skies above the UK, including things like satellites. It will complement an existing network of 30 video cameras called the <a href="https://ukmeteornetwork.co.uk">UK Meteor Observation Network</a>, which is already run by citizen scientists to spot fireballs and smaller meteors. UKMON focuses on capturing images rather than meteorite recovery. The two operations will share data, enhancing one another’s abilities. There are also plans to extend the new network to the US, South America, New Zealand and Saharan Africa in the next few years. </p>
<p>The challenges facing the UK operation are quite different to those in Australia. Where the Australian network needs to be able to survive unattended in the brutal desert heat, the UK cameras will work in a distinctly colder, wetter climate. </p>
<p>They will have to contend with light pollution, unpredictable weather and significant cloud cover, reducing the number of nights they will be able to take images. But most problematic of all is the ground itself. The Australian outback is ideal for meteorite hunting: uniformly red and with very little vegetation, meaning you can spot a little black rock from several hundred metres. By contrast, the UK’s lush vegetation and woodland can easily camouflage meteorites.</p>
<p>Yet the UK network also has advantages. Most cameras will be within a day’s drive and connected to the internet to provide instant warnings when a camera needs some tender loving care – the Australian cameras tend to be on rougher terrain that takes longer to reach and many are not internet-connected. At the same time, the UK population density is such that quite a lot of people are likely to spot a large fireball and take pictures on their smartphones. </p>
<h2>Apps upside your head</h2>
<p>Unlocking the assistance of these 65m independent autonomous observatories in the UK is part of the project. The Australian fireball team has developed an app in conjunction with US software consultancy ThoughtWorks. Known as Fireballs in the Sky and free for <a href="https://itunes.apple.com/gb/app/fireballs-in-the-sky/id709019924?mt=8">Apple</a> and <a href="https://play.google.com/store/apps/details?id=com.tw.fireballs&amp;hl=en_GB">Android</a> phones alike, it allows anyone to become a citizen scientist. Users can report any fireball, as well as getting details of the next big meteor shower and where in the sky to look for it – and here’s a grab of what it looks like.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182827/original/file-20170821-4938-lfmj1h.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182827/original/file-20170821-4938-lfmj1h.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The app.</span>
<span class="attribution"><span class="source">DFN/ThoughtWorks</span></span>
</figcaption>
</figure>
<p>The app is already up and running. In fact, the latest recovered meteorite in Australia, called Dingle Dell, was <a href="http://www.abc.net.au/news/2016-11-22/meteorite-recovered-with-the-help-of-dedicated-star-gazers/8046880">initially observed</a> by a citizen scientist using it. </p>
<p>This made it possible to find the pristine meteorite before delicate minerals inside it were irreparably altered or washed away by rain, revealing extraterrestrial salts formed early in the solar system that usually quickly disappear on the surface of Earth. These could potentially tell us things about the origins of life and water on our planet. </p>
<p>These kinds of exciting discoveries give a taste of why it will be a race against time to recover the first meteorite tracked by the UK network. So do we have any volunteers?</p><img src="https://counter.theconversation.com/content/82798/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Daly’s PhD was funded under The Australian Research Council Laureate fellowship awarded to Professor Phil Bland. Luke is an associate of the Royal School of Mines at Imperial College London, and a member of the Meteoritical Society.</span></em></p><p class="fine-print"><em><span>Gareth Collins has received funding from the UK Research Councils (NERC, STFC &amp; EPSRC).</span></em></p><p class="fine-print"><em><span>Martin Suttle receives funding from the STFC. </span></em></p>Ten new remote cameras will soon be scouring the British night skies for meteorites.Luke Daly, Research Associate, School of Geographical and Earth Sciences, University of GlasgowGareth Collins, Reader in Planetary Science, Imperial College LondonMartin Suttle, Researcher in Meteoritics and Planetary Science, Imperial College LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/825122017-08-18T05:03:33Z2017-08-18T05:03:33ZFrom the edge of the Solar System, Voyager probes are still talking to Australia after 40 years<figure><img src="https://images.theconversation.com/files/182362/original/file-20170817-16233-1tfxoku.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">Both Voyager spacecraft are only in communication with Earth via a Canberra tracking station.</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>This month marks 40 years since NASA launched the two Voyager space probes on their mission to explore the outer planets of our Solar System, and Australia has been helping the US space agency keep track of the probes at every step of their epic journey.</p>
<p>CSIRO operates NASA’s tracking station in Canberra, a set of four radio telescopes, or dishes, known as the Canberra Deep Space Communication Complex (<a href="https://www.cdscc.nasa.gov/">CDSCC</a>).</p>
<p>It’s one of three tracking stations spaced around the globe, which form the <a href="https://deepspace.jpl.nasa.gov/">Deep Space Network</a>. The other two are at <a href="https://www.gdscc.nasa.gov/">Goldstone</a>, in California, and <a href="https://www.mdscc.nasa.gov/index.php?ChangeLang=en">Madrid</a>, in Spain. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182364/original/file-20170817-16209-lr9vy4.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182364/original/file-20170817-16209-lr9vy4.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The Canberra Deep Space Communication Complex (CDSCC).</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>Between them they provide NASA, and other space exploration agencies, with continuous, two-way radio communication coverage to every part of the Solar System. </p>
<hr>
<p><em><strong>Read more:</strong>
<a href="https://theconversation.com/water-water-everywhere-in-our-solar-system-but-what-does-that-mean-for-life-76315">Water, water, everywhere in our Solar system but what does that mean for life?</a></em></p>
<hr>
<p>Four decades on and the Australian tracking station is now the only one with the right equipment and position to be able to communicate with both of the probes as they continue to push back the boundaries of deep space exploration.</p>
<h2>The launch of Voyagers</h2>
<p>The <a href="https://www.jpl.nasa.gov/voyager/mission/">Voyagers’ primary purpose</a> was to fly by Jupiter and Saturn. If all the scientific objectives were met at Saturn, then Voyager 2 would be targeted to continue on to Uranus and Neptune.</p>
<p>At each planetary encounter – running on power equivalent to the light bulb in your refrigerator – the Voyagers would transmit photographs and scientific data back to Earth before being accelerated towards their next target by the planet’s gravity, like a slingshot.</p>
<p>Timed to take advantage of a favourable alignment of the outer planets not expected to recur for another 175 years, Voyager 2 launched first on August 20, 1977, followed by Voyager 1 on September 5. Although launched second, Voyager 1 was sent on a faster trajectory and was timed to arrive at Jupiter ahead of Voyager 2. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182365/original/file-20170817-16222-2j23u0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182365/original/file-20170817-16222-2j23u0.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Voyager 2 launches aboard Titan-Centaur rocket.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>When Voyager 1 arrived at Jupiter in 1979 the mission’s scientific discoveries began.</p>
<h2>Jupiter revealed close up</h2>
<p>The world watched as the Voyagers’ cameras sent back – via the tracking stations – close up images of Jupiter and its moons, letting us see these worlds in detail for the very first time. </p>
<p>From the turbulence surrounding huge storms on Jupiter, to a volcano erupting on Jupiter’s moon Io, to hints that the icy surface of Europa probably conceals an ocean underneath, the Voyager mission started to reveal the outer Solar System to us in inspiring detail.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182371/original/file-20170817-13444-1301l19.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182371/original/file-20170817-13444-1301l19.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Getting close to the Jupiter.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182372/original/file-20170817-13501-1jy19nt.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182372/original/file-20170817-13501-1jy19nt.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Peering into Jupiter’s famous red spot.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182373/original/file-20170817-13480-lq7fqz.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182373/original/file-20170817-13480-lq7fqz.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Voyager 1 captures a volcanic eruption on Jupiter’s moon Io.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182366/original/file-20170817-15619-60go96.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182366/original/file-20170817-15619-60go96.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Voyager 1 image of Ganymede, Jupiter’s largest moon and the largest moon in the Solar System at 5,262km in diameter (compared to Earth’s Moon at 3,475km diameter).</span>
<span class="attribution"><span class="source">NASA/JPL/Image processed by Bjӧrn Jόnsson</span></span>
</figcaption>
</figure>
<p>Indeed, during the course of their 12-year mission, the Voyagers discovered 24 new moons orbiting the outer planets and refined NASA’s use of the Deep Space Network to listen to signals from distant spacecraft.</p>
<h2>To Saturn and beyond</h2>
<p>After Jupiter, both Voyagers went on to encounter Saturn. Voyager 1 achieved the major goal of closely approaching Saturn’s giant moon, Titan. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182375/original/file-20170817-13469-vt878q.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182375/original/file-20170817-13469-vt878q.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Both Voyagers passed by the ringed planet Saturn.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>Following this encounter, with its primary mission ended, Voyager 1 was flung on a northward trajectory above the plain of the orbits of the planets. Voyager 2 was subsequently targeted to travel outward on an extended mission to visit the next two gas giant worlds.</p>
<p>When Voyager 2 flew past Uranus in January 1986, the signals being received were much weaker than when it flew by Saturn, five years earlier. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182382/original/file-20170817-13444-wbh9xl.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182382/original/file-20170817-13444-wbh9xl.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Voyager 2 captures Uranus.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>Consequently, CSIRO’s radio telescope at Parkes was linked, or arrayed, with NASA’s dishes in Canberra to boost Voyager 2’s weak radio signal.</p>
<p>This was the first time an array of telescopes had been used to track a spacecraft. Yet this array would be insufficient to receive the even fainter signals expected when Voyager 2 reached Neptune in 1989.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182537/original/file-20170818-28120-3yf8fv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182537/original/file-20170818-28120-3yf8fv.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">CDSCC staff at Parkes monitoring the encounter with Uranus’ moon, Miranda, in 1986.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>So in the time between the encounters, NASA expanded Canberra’s largest dish from 64 metres to 70 metres in diameter to increase its sensitivity, and then linked it again with the Parkes 64 metre dish, to maximise the data capture at Neptune. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182378/original/file-20170817-13430-t2hfq7.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182378/original/file-20170817-13430-t2hfq7.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Neptune’s bright wispy cirrus-type clouds can been seen against the blue atmosphere.</span>
<span class="attribution"><span class="source">NASA/JPL/ Image processed by Bjӧrn Jόnsson</span></span>
</figcaption>
</figure>
<p>The increased size and sensitivity of the Canberra dish also meant that it was able to support Voyager’s ongoing journey beyond the outer planets.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182539/original/file-20170818-30283-fivs8d.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182539/original/file-20170818-30283-fivs8d.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">Robina Otrupcek tracking Voyager 2 at Neptune from the CSIRO Parkes telescope on the day before the close approach in 1989.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>The Pale Blue Dot</h2>
<p>In 1990 Voyager 1 turned its cameras towards home. The resulting photograph, known as the Pale Blue Dot, is our most distant view of Earth, a fraction of a pixel floating in a deep black sea. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182376/original/file-20170817-13501-t0lmj2.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182376/original/file-20170817-13501-t0lmj2.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">This pale blue dot, less than a pixel in size, is Voyager 1’s view of Earth.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>The legendary astrophysicist Carl Sagan, involved with Voyager since its inception, reflected that this distant view of the tiny stage on which we play out our lives should inspire us “to preserve and cherish that pale blue dot, the only home we’ve ever known”.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wupToqz1e2g?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The Pale Blue Dot.</span></figcaption>
</figure>
<p>Both Voyagers have long since left the outer planets behind, two explorers heading into the galaxy in different directions, still sending data back to Earth and answering questions we didn’t even know to ask when they were launched 40 years ago.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="http://theconversation.com/the-pale-blue-dot-and-other-selfies-of-earth-39118">The pale blue dot and other 'selfies' of Earth</a>
</strong>
</em>
</p>
<hr>
<h2>Voyagers only talk to Australia</h2>
<p>The Canberra tracking station continues to receive signals from both Voyager spacecraft every day, and is currently the only tracking station capable of exchanging signals with Voyager 2, owing to the spacecraft’s position as it heads on its southward path out of the Solar System.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182383/original/file-20170817-13501-5sxt70.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182383/original/file-20170817-13501-5sxt70.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The Parkes telescope tracking Voyager 2 at Neptune on the day of the close approach.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>Due to their respective distances, tens of billions of kilometres from home, the signal strength from both spacecraft is very weak, only one-tenth of a billion-trillionth of a watt.</p>
<p>In 2012, Voyager 1 became the first spacecraft to have entered interstellar space, the region between the stars. Lying beyond the influence of the magnetic bubble generated by our Sun, Voyager 1 is able to directly study the composition of the interstellar medium, for the first time.</p>
<p>Voyager 1 is still receiving commands that can only be sent from Canberra’s dishes. It is the only station with the high-power transmitter that can transmit a signal strong enough to be received by the spacecraft.</p>
<p>It has been an epic voyage for two spacecraft no bigger than small buses, two brilliant robots with an eight track tape deck to record data and 256kB of memory.</p>
<h2>A golden message</h2>
<p>The scientists and engineers at NASA’s Jet Propulsion Laboratory in California, who built the Voyagers and continue to operate them, planned ahead for Voyager’s legacy and its journey beyond our Solar System. </p>
<p>On board both spacecraft they placed a golden record, similar in concept to a vinyl record, featuring one and a half hours of world music and greetings to the universe in 55 different languages.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182386/original/file-20170817-13469-1geh4xq.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/182386/original/file-20170817-13469-1geh4xq.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The golden record and instructions on how to play it.</span>
<span class="attribution"><span class="source">NASA/JPL</span></span>
</figcaption>
</figure>
<p>The cover art features a pictorial representation of how to play the record and a map reference to Earth’s location in our galaxy based on the positions of surrounding pulsars.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Bhuq9rNO_FQ?wmode=transparent&amp;start=0" frameborder="0" allowfullscreen></iframe>
<figcaption><span class="caption">The first of the 31 recordings. Click on the video to hear the rest.</span></figcaption>
</figure>
<p>By 2030, both Voyagers will be out of power, their scientific instruments deactivated, no longer able to exchange signals with Earth. They will continue on at their current speeds of more than 17 kilometres per second, carrying their golden records like messages in bottles across the vast ocean of interstellar space. </p>
<p>Heading in opposite directions, southward and northward out of the Solar System, it will be 40,000 years before Voyager 2 passes within a handful of light years of the closest star system along its flight path, and 296,000 years before Voyager 1 passes by the bright star Sirius.</p>
<p>Beyond that, we may imagine them surviving for billions of years as the only traces of a civilisation of human explorers in the far reaches of our galaxy.</p><img src="https://counter.theconversation.com/content/82512/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Voyager space probes sent back some amazing images of the planets in the outer Solar System, and they're still talking to Earth every day via Australia's tracking station.John Sarkissian, Operations Scientist, CSIROEd Kruzins, Facilities Program Director Nasa Operations Canberra Deep Space Communication Complex , CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/813082017-08-03T21:10:14Z2017-08-03T21:10:14ZWhen the sun goes dark: 5 questions answered about the solar eclipse<figure><img src="https://images.theconversation.com/files/179092/original/file-20170720-32541-ncrgek.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=496&amp;fit=clip" /><figcaption><span class="caption">NASA&#39;s projection of the August 21 solar eclipse.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/4390">NASA</a></span></figcaption></figure><p><em>Editor’s note: A total solar eclipse will be visible across the U.S. on Monday, August 21. Shannon Schmoll, director of the Abrams Planetarium at Michigan State University, explains why and how it happens, and what we can learn from an eclipse.</em></p>
<p><strong>How do we know when an eclipse is going to happen? How do we know in advance where it will be visible?</strong></p>
<p>Solar eclipses happen when our view of the sun is blocked by the moon. When the moon lines up between the sun and Earth, the moon will cast a shadow onto Earth. This is what we on the ground observe as a solar eclipse.</p>
<p>We know <a href="https://eclipse.gsfc.nasa.gov/eclipse.html">when they’ll happen</a> because over centuries <a href="https://spaceplace.nasa.gov/review/dr-marc-solar-system/planet-distances.html">astronomers have measured very precisely</a> the motions of the Earth, moon and sun, including their orbital shapes, how the orbits <a href="https://en.wikipedia.org/wiki/Precession">precess</a> and other parameters. With those data about the moon – and similar information about the <a href="http://curious.astro.cornell.edu/about-us/41-our-solar-system/the-earth/orbit/87-how-do-you-measure-the-distance-between-earth-and-the-sun-intermediate">Earth’s orbit around the sun</a> – we can make mathematical models of their movements in relation to each other. Using those equations, we can <a href="https://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html">calculate tables of data</a> that can <a href="https://eclipse.gsfc.nasa.gov/SEpubs/5MKSE.html">predict what we will see on Earth</a>, depending on location, during an eclipse as well as when they will happen and how long they last. (The next <a href="https://eclipse.gsfc.nasa.gov/SEpubs/5MCSE.html">major solar eclipses</a> over the U.S. will be <a href="https://eclipse.gsfc.nasa.gov/5MCSE/5MCSE-Maps-10.pdf#page=28">in 2023 and 2024</a>.)</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179271/original/file-20170721-28478-zo0p8i.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/179271/original/file-20170721-28478-zo0p8i.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">The path of the eclipse on August 21.</span>
<span class="attribution"><a class="source" href="https://eclipse.gsfc.nasa.gov/SEmono/TSE2017/TSE2017.html">NASA</a></span>
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</figure>
<p><strong>How often do eclipses happen?</strong></p>
<p>A solar eclipse happens, on average, a couple times a year. The <a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">moon passes between the Earth and sun</a> every 29 days, a time we call the “<a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html">new moon</a>” – when the moon is not visible in Earth’s nighttime sky. However, the moon’s orbit and the sun’s path in our sky don’t match up exactly, so at most of those new moon events, the moon appears above or below the sun.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179078/original/file-20170720-6436-q7fdr5.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip">
<figcaption>
<span class="caption">The blue line shows the ecliptic, the path the sun appears to take in our sky as viewed from Earth. The white line shows the moon’s orbit. For eclipses to happen, both the sun and the moon need to be within the area marked with yellow brackets.</span>
<span class="attribution"><span class="source">John French, Abrams Planetarium</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Twice a year, though, there is a period where the moon and the sun line up with Earth – astronomers call this an eclipse season. It lasts about 34 days, long enough for the moon to complete a full orbit (and then some) of the Earth. During each eclipse season, there are at least two eclipses visible from some parts of the Earth. At the full moon, there will be a lunar eclipse, when the moon passes directly behind the Earth, resulting in a darker, reddish-colored moon. And at the new moon, there will be a solar eclipse, when the sun is blocked by the moon. </p>
<p><strong>Can we learn anything from eclipse events, or are they really just oddities that happen in nature?</strong></p>
<p>We can definitely learn things from eclipses. The outermost layer of the sun, known as the corona, is difficult to study because it’s less bright than the rest of the sun – so we have trouble seeing it amid the rest of the sun’s brightness.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip"></a>
<figcaption>
<span class="caption">During an eclipse the sun’s corona becomes visible to observers on Earth.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/white_light_corona.jpg">NASA</a></span>
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<p>When the moon blocks the sun, we can see the corona, the famous visual of the halo of light around the dark disk of the moon. Currently astronomers study this by creating an artificial eclipse with a mask built into special instruments on telescopes called coronagraphs. This is great, but doesn’t allow the best pictures. Eclipses give scientists opportunities to get more data to <a href="https://www.nasa.gov/feature/goddard/2017/eclipse-2017-nasa-supports-a-unique-opportunity-for-science-in-the-shadow">study the corona in depth</a>.</p>
<p>We can also learn about Earth itself. In an area affected by an eclipse, the darkening of the sun leads to a <a href="https://sunearthday.nasa.gov/2006/faq.php">sudden drop in temperature</a>. NASA-funded studies during this eclipse will look at the effects from the eclipse on our atmosphere as well as what happens on land. Previous studies observed animal behavior during an eclipse in 2001 and noted <a href="https://academic.oup.com/astrogeo/article-pdf/42/4/4.4/436602/42-4-4.4.pdf">some animals went through their night routines</a> as the sun disappeared while others became nervous.</p>
<p>And we can learn about the whole universe. Less than 100 years ago, an eclipse proved a prediction Albert Einstein had made about gravity. That success helped make him a household name. In his <a href="https://asd.gsfc.nasa.gov/blueshift/index.php/2015/11/25/100-years-of-general-relativity/">general theory of relativity</a>, Einstein had predicted that <a href="https://eclipse2017.nasa.gov/testing-general-relativity">gravity could bend the path of light</a>. The effect he predicted was very slight, so it would best be viewed as the light passed a very large celestial body as part of its travels across a very long distance of space.</p>
<p><a href="http://adsabs.harvard.edu//full/seri/ApJ../0101//0000133.000.html">Sir Arthur Eddington</a>, an astronomer who helped further the study of general relativity and whose work is a major piece of our modern understanding of stars and black holes, used the <a href="http://dx.doi.org/10.1098/rsta.1920.0009">darkness provided by a solar eclipse</a> to look at the position of the stars’ light during the day, when it passed the sun. He then <a href="https://www.wired.com/2009/05/dayintech_0529/">compared those positions to their known positions at night</a>. He saw that <a href="https://sunearthday.nasa.gov/2006/events/einstein.php">the gravity of the sun had bent the path</a> – exactly as, and in the precise amount that, Einstein had predicted.</p>
<p><strong>How weird is it that the moon can basically exactly block out the sun?</strong></p>
<p>It is very unusual that the moon and the sun just happen to be at <a href="http://www.astronomy.com/magazine/ask-astro/2000/10/why-is-the-moon-exactly-the-same-apparent-size-from-earth-as-the-sun-surely-this-cannot-be-just-coincidence-the-odds-against-such-a-perfect-match-are-enormous">the right distances and sizes</a> to <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/understand_size.html">appear to have the same size</a> in our sky. This allows the moon to perfectly block the sun’s disk, while also showing us the corona. Venus and Mercury, for instance, can also pass in front of the sun from our perspective. However, they appear as small specks moving across the sun.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img alt="" src="https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=237&amp;fit=clip"></a>
<figcaption>
<span class="caption">Venus appears as a small dot in the upper left as it passes between the sun and Earth in 2012.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/IOTD/view.php?id=78196">NASA</a></span>
</figcaption>
</figure>
<p><strong>What would someone standing on the moon see happen on Earth? Would Earth get dark?</strong></p>
<p>If you were on the moon, you would be able to see the effects of the solar eclipse on Earth only if you were standing on the moon’s night side, the side facing the Earth. You would see a round shadow cast onto the Earth. This particular eclipse will first hit the Pacific Ocean, then move into Oregon, cross the U.S. to South Carolina and end in the Atlantic Ocean. This path the shadow takes is called the path of totality. </p>
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<p class="fine-print"><em><span>Shannon Schmoll does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>An astronomer explains how and why – and when – eclipses happen, what we can learn from them, and what they would look like if you were standing on the moon.Shannon Schmoll, Director, Abrams Planetarium, Department of Physics and Astronomy, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.